The problems is consistency. But you'll see that in anybody here that sides with a particular political party. I mean, just looks at the division within the Republican party. This is to be expected.
A lot of libertarians though, and it's frustrating to me, aren't just inconsistent in their beliefs... but they downright contradict themselves sometimes. The immigration issues is a big one too, how can you support the free market but not support an influx of cheap labor? Hell, even W at one point said that he supported immigration for this reason. Of course large MW increases will work in direct contradiction of this.. but I believe more business owners will be paying under the table as a result.
Or the legalizing of marijuana is another one.... I'm all for the decriminalization, but I'm not jumping on the "make a legitimate business out of it so the government can tax you" BS. I'm more about emptying out prisons and easing the burden on the court system and taxpayers, not finding another reason for the government to tax people.