But then again they do legitimately support civil liberties and aren't at all nationalistic.
This has not been my experience. Most of the (modern American) libertarian intellectual patron saints, like Ludwig von Mises, Ayn Rand, and Murray Rothbard, were quite open racists and sexists. And even the ones who aren't nationalists tend to believe in human inequality, demarcated by something like IQ rather than race or culture. After all, the successful among us are simply our betters, and attempts to enforce any kind of social equality are tyrannical because try as we might we just can't make everyone the same. Almost without exception, right-libertarians I've interacted with have had right-wing views about social issues.
The authoritarianism extends only to protecting property. That really is quite different from fascism.
Meh. More issues than you might think are relevant to "protecting property." Libertarians have traditionally opposed the civil rights movement, for example, on the basis of protecting the prerogatives of private property owners. They oppose feminism on similar grounds- contracts are sacrosanct, and the state enforcing all this "equal treatment and equal pay" nonsense is a form of tyranny.
This is really the only "new" thing about the modern American libertarian movement. It's perfectly in keeping with the long right-wing political tradition stretching back the French Revolution - what it adds is the insistence that there is something insurgent, something rebellious, about what is essentially a defense of power and privilege.
Increasingly, I am seeing the two-spectrum model for politics as actually worse than a single-spectrum model. Economic and social issues can't be so readily separated. And frequently economic issues are simply a proxy or cipher for how someone believes
society should work. As an example, the early classical liberals were 'left-wing' in the sense that they wanted free markets because they believed free markets would lead to social equality. Modern free-marketers tend to be right-wing because they believe free markets give proper scope to what they see as natural
inequalities between people, whereas "government tyranny" always results from attempts to make equal what can never truly be equal. Free-market politics are as often about reinforcing social inequalities of various kinds as they are about free markets for their own sake.