[Mark Bahner]

"Take abortion, for instance. There are Libertarians for Life, and there are Pro-Choice libertarians."

Yes, just as you'll find Republicans who are for life, and for choice. And you'll find Democrats who are for life, and for choice.

But look at the vast majority of other issues, e.g., the War on Some Drugs, federal spending on education, federal aid to agriculture...and you'll find much more solidarity of opinion among Libertarians than among Republicans. The Libertarian Party is much more ideologically consistent than the Republican Party. Which is easy to do, since the Republican Party isn't ideologically consistent at all.

[HumanaeVitae]

Well, this isn't about Republicans or Democrats or capital "L" Libertarians. It's about definitions. Again, if you and I disagree on what the idea "liberty" entails, then how are you going to form a society around that "idea"?
By the way, this also works on collectivists with things like "equality". In fact, it works against all Leftists--including libertarians.