Uttering the cliche that "what Islam needs is a Reformation" merely shows that the speaker understands neither Islam nor the Reformation.
The Protestant Reformation was the rejection of traditional accretions in favour of the authority of scripture; an attempt to return to "original" Christianity. Islam has experienced waves of such reformism throughout its history, also based on the authority of scripture and seeking to return to "original" Islam. (To understand Islam, you need to understand its history; A History of Islamic Societies by Ira Lapidus is an excellent starting point.)
The Reformation saw a dramatic upsurge in religiously-motivated violence in both scale and intensity. Even in its very earliest periods, Islam was wracked by assassinations and civil wars while the current period is marked precisely by an upsurge in religiously-motivated violence. Again, what is problematic about contemporary Islam is what is more like the Reformation not less.
Indeed, the most fundamentalist Protestant understanding of the nature and authority of Scripture is a pale shadow of the status and authority mainstream Sunni Islam puts on the Quran. Cristian fundamentalism says that the Bible is the inerrant word of God, but the word of God situated in time and mediated through inspired individuals. Thus, the Gospel of Luke is Luke reporting the word of God.
The eternal word
The mainstream Sunni interpretation of the Quran is that it is eternal--not created in time at all--and is the direct word of God mediated by nothing. This gives the Quran a standing and authority which far surpasses what even the most avid Christian fundamentalist gives scripture. Indeed, the hadith are more like the Christian understanding of scripture than is the mainstream Sunni understanding of the Quran.
This mainstream Sunni interpretation of the Quran arose out of the Mu'tazilite v Asharite debates of the C8th to C10th. (A useful discussion of which is provided here.) The effect of the (winning) Asharite understanding was to restrain the power of the Caliph, the ruler, as it put the Quran beyond the human and so left religious understanding--and, indeed, law--in the hands of the community of scholars (the ulama) and the Muslim community generally (the ummah); not any individual, no matter how elevated. The Quran was utterly above any human authority and so study of it provided access to an authority which trumped any (other) authority. The notion that democracy is blasphemous because it puts law-making authority in the hands of mere people flows from this outlook.
It was, however, a classic case of ideas having consequences, since the debate was about the standing of reason and revelation. The winning Asharite interpretation put revelation absolutely above reason and the unfettered Will of God as the grounding of everything. Abū Ḥāmid Muḥammad ibn Muḥammad al-Ghazālī (c.1058-1111) or al Ghazali put together what became the overwhelmingly dominant synthesis within the Sunni mainstream which essentially elevated jurisprudence (the rules established by the Will of God and adherence to which marks submission to the Will of God) as the form of Islamic religious reasoning.
Al Ghazali's synthesis was rebutted by Abū l-Walīd Muḥammad bin ʾAḥmad bin Rued (1126-1198) or Averroes, but the rebuttal had effectively no influence within Islam. Averroes's Aristotelianism did, however, have a great deal of influence within Latin Christendom (Aquinas referred to Aristotle as "the Philosopher" and Averroes as "the Commentator"). The Islamic debate over reason and revelation was largely a debate over incorporating not merely the techniques (which al Ghazali happily used) but the understandings of Greek philosophy within Islam.
What folk are trying to say when they say "Islam needs a Reformation" is "what Islam needs is the Enlightenment reaction to the Reformation". That reaction being to dethrone political theology as the dominant forms of justification and legitimation, to put religion in a box and to turn the relationship between people and the world (and between people) into the source of justification and legitimation.
Well, yes, but the Enlightenment did not come out of nowhere. It was built in part on the Scientific Revolution and in part was yet another round of wrestling with the Classical heritage. (Not that these two things were mutually exclusive: if Lucio Russo is correct, the Scientific Revolution was partly the rediscovery of the Hellenistic Scientific Revolution.)
Which puts the Enlightenment well within the recurring patterns of Latin Christendom-cum-Western Civilisation of periodic upsurges in wrestling with said heritage--as in the Carolingian Renaissance, the Renaissance of the C12th, The Renaissance. All of which were based on the notion that said heritage had standing and authority.
Which is exactly what al Ghazali's synthesis denied. It was fine to use the techniques of Greek philosophy (and logic and mathematics) but only within, and at the service of, revelation.
Latin Christendom and Judaism also had very similar debates over Aristotelianism, reason and revelation as did Islam, but in each of their cases, the great synthesiser--Thomas Aquinas (1225-1274) for Latin Christendom, Mosheh ben Maimon or Maimonides (1125-1204) for Judaism--upheld Aristotelianism and provided a marriage of reason and revelation. Faith, but not without reason.
Neither synthesiser did so without controversy and resistance from fellow believers. There were budding al Ghazali's within both Latin Christendom and Judaism; the temptation to place revelation uber alles is inherent in monotheism. Both Judaism and Christianity, however, had factors mitigating against the temptation. The permanent minority status of the Jews likely helped to entrench a perspective about limits built into the nature of things.
Aquinas was assisted by Christ acknowledging secular authority ("render unto Caesar"), that Paul of Tarsus used natural law reasoning along with a history of interpreting scripture within the limits of wider truth (given that scripture was the indirect creation of God but the world was His direct creation). So being born before Christ was an excuse for not following the Christian understanding of God as revelation was an unfolding process located in time.
All of which were products of Christianity starting its existence as a powerless, minority religion which was required to argue its case for centuries before achieving secular power. For both Judaism and Latin Christendom, law-with-authority which was not religious law was an established fact of life. The Catholic/Orthodox understanding of scripture as the product of the Church (understood as the community of believers) is a world away from the mainstream Sunni understanding of the Quran.
Islam, by contrast, went straight from revelation to political power to empire within a single lifetime. (The Muslim calendar dates from Muhammad's flight to Medina, so his achievement of political power.) Muslim authority came from submission to God. To elevate revelation was to elevate the community of believers (the ummah) over non-believers and religious scholars (the ulama) over other sources of authority. Appealing to collective egoism (even narcissism) has considerable appeal. Moreover, law was religious law. Certainly there were rulers, but their status was always somewhat dubious--they typically claimed to be agents of the (or later a) caliph. And those rulers (even the caliph) were not law-givers in the normal sense--their decrees were more like by-laws, operating as strictly subordinate to Sharia.
Moreover, since the Quran was outside time, there was never any excuse for failing to be Muslim. There had only ever been one Revelation, the Jews and Christians had willfully misconstrued it.
Revelation was central to the operation of authority within Islamic societies far more profoundly than in Jewish communities subject to the authority of outsiders or in Christian states where law, even canon law, was a human construction.
For Asharite thinkers, putting any limits on Allah, on God, was to limit His utterly transcendent nature and authority. Even the limit of working through inherent structures in the world. Al Ghazali denied that there was any causality beyond the Will of God; Allah remade the world at every moment, and could do so any way He wished.
It is hard to have a Scientific Revolution if causality is merely the Will of God, which it is blasphemous to put any structure upon. The best science can hope to do is to describe God's habits so far.
While Islamic science did not entirely die once al Ghazali's synthesis became dominant, it did become something of a pale shadow of its former self. Apart from the metaphysical difficulties, if one was intellectually inclined, it was safer and easier to apply oneself to religious learning. Especially as there was status and income to be had as an interpreter of Sharia.
For Islam to go through its own Enlightenment, the problem is finding a way in in to unpick the straightjacket of revelation and capricious divine will. Mainstream Christianity accepted that God was, in effect, a constitutional monarch who created via fundamental structures. That something was not Good because God did it, but that God did it because it was Good. The nature of things, including the nature of morality, of law, of political authority, had existence outside of revelation and God's Will--for even God's Will operated according to patterns and structures.
Conversely, al Ghazali's synthesis said that whatever God did was Good, that there is no Good to investigate outside of what God chooses to Will. Just as there was no structure to the universe outside of what God happens to decide from moment to moment. Hence justification and legitimation can only be grounded in revelation. Where is the way in for any other understanding of the role of religion and legitimate authority?
Been there, done that
Islam has a recurring pattern of struggles between reformers--who want to go back to the only source of real authority, the C7th revelations at the heart of Islam--and modernisers--who want to incorporate the insights of outsiders. The Mu'tzalites were modernisers just as the Islamists and jihadis of our time are reformers.
Generally, the modernisers lose. The insights of outsiders are, after all, infidel insights. To give them standing over Islam itself is to undermine the status of the Muslim community, the ummah, and the authority of the ulama, the gatekeepers of righteousness.
Social scientists talk about things being path dependent. Islam is gripped by powerful path dependence.
As Islam grapples with the modern world, it is foolish to underestimate how fraught that is. What Islam needs is not yet-another-Reformation; they have had far too many of those and those who want yet another Islamic Reformation are precisely the problem. What Islam needs is its own Aquinas or Maimonedes. A thinker or thinkers who can create a synthesis that can provide a way in for avenues of authority and understanding which are not bound by C7th revelations deemed to be outside time and so utterly superior to, and unbound by, anything within it. (Aquinas lived in the C13th of the Christian era; we are currently in the C15th--the year 1434 AH--of the Islamic era, so they are perhaps overdue.)
Islam does not merely need its own Enlightenment, it needs its own synthesising precursor of such, so an Enlightenment within the civilisation of Islam is possible. With added difficulty that holders of religious authority in Islam know precisely where that led for Christendom and Judaism and many of them are perfectly happy to recommend killing anyone who defies God's authority (and therefore their own).
Islamic clerics can appeal to the egoism and collective narcissism of their congregations (where collective convenience really is the shared reality principle; that tends to be self-policing). Conversely, any putative Aquinas or Maimonedes has to sell humility. That there is some legitimacy to infidel success and perspectives. Not exactly an even sell.
[Previously posted at Skepticlawyer.]
[Previously posted at Skepticlawyer.]