Conservatives are typically bad (sometimes very bad) on how existing structures fail for particular groups: particularly groups that it is “traditional” they fail for. That is, conservatives typically have a much stronger sense of achievement for existing structures than their sense of failures of the same.
Progressivists are typically bad on how existing structures work well. That is, they have a sense of failures but a typically flawed sense of achievement.
Libertarians typically fail to consider what might be called “second order” social dynamics: that we are not random individuals but members of wider collectivities that have their own dynamics and demands.
Goldwater and Rand Paul in their attitudes to the 1964 Civil Rights Act seem to be typifying the way libertarians of conservative bent (or conservatives of libertarian bent) fail. Particularly given how much the African-American experience gets in the way of a triumphal view of the American project.
On the notion of Goldwater as hero, personally, I do not understand why people need “heroes” in the unblemished sense. You can admire some aspects of a person and not others. (It is worth reading the comments thread on Yglesias's post on Goldwater to see just how screwed up Americans get over race.)
As for morally judging the past, we cannot “unwind” how people’s sense of right and wrong has evolved since whenever, but we can consider whether there were people at the time who called the issue correctly. If there were, then that puts those who did not in a poorer light.
On the conservative/liberal split in the context of US politics, Scott Sumner puts it like this:
Conservatives tend to be nationalistic, which makes them over-rate America. Liberals know more about American sins than they do about the sins of others during earlier centuries (including our victims) which is why they under-rate America.A point which has wider application.
ADDENDA: A friend has sent the following comment:
Reading the intro to your post reminded me of Ambrose Bierce's definition in The Devil's Dictionary:
"Conservative - one who is enamoured of existing evils, as opposed to the liberal, who wishes to replace them with others."
Bierce's primary definition of politics - "a strife of interests masquerading as a contest of principles" - is deservedly well-known, but his secondary definition deserves to be better known than it is: "the conduct of public affairs for private advantage". Plus ça change ...