Premise 2: Liberty alone is an insufficient basis of a practical ideology.
Yeah, you haven't shown this, and there are problems with other premises. But also, some of the argument doesn't follow.
Conclusion 2: Most Libertarians do not want Pure Libertarianism.
Even if we accept premise 2, we don't have conclusion 2. Wanting a practical ideology doesn't mean not wanting a pure ideology. Libertarians would love an AnCap society, for as long as it lasted. To ensure it lasts, people are fine making compromises, but that doesn't mean they don't want the perfection. It's just impossible to have and keep it.
Conclusion 3: Most libertarians add other ideologies to get a more practical ideology.
Conclusion 3 is wrong as well. At the very least, it does not follow, and observationally, I'm skeptical of it. Many people who advertise themselves as libertarians aren't, like Mo Brooks for example. I know a guy from the Libertarian Party of AL who talked to Mo Brooks, who said we're on the same side and that he's basically a libertarian. No, Mo Brooks is just an authoritarian that isn't in power. Mo Brooks maybe (I doubt it, but beyond scope) could be considered Libertarian + Conservatism, but he is not a conservative libertarian, as he fails to uphold basic NAP principles.
Also, most of the Libertarians I know are just basic bitch Libertarians. I do know some that add other things, but most of us are primarily Libertarians, and the ones that do add something extra don't do it out of a failure of libertarianism, but because they are religious.
But also, there's a huge problem with the entire argument itself. Namely, the difference between 'pure libertarianism' and 'practical libertarianism'. The difference here is
not a philosophical one, or at least a very minor one. It's an implementation question: how does one create a NAP-centric society that lasts? All libertarians must, by definition, be onboard with trying to obey the NAP as best as possible, so they all believe in the same ideal, the NAP.
Basically, even the 'practical' libertarian must also be a pure libertarian in prioritizing the NAP.
Some decide to add stuff to this ideal. That is usually fine, as long as the NAP still has priority. If they'd violate the NAP because of other ideals, they are no longer a libertarian.
But some of the examples you've shown? They violated (or advocated for a society that would violate) the NAP because of those other ideals. They are thus not libertarians. For example:
Like, a Christian Libertarian believes in a Christian end, and believes a libertarian methodology would be effective to achieve that end, and their belief of that end informs where they think the boarders of that methodology lie. A Christian, for example, is likely not going to be in favor of particularly liberal divorce laws.
See, the above wouldn't be a libertarian for 2 reasons. First, they are only following a libertarian methodology, they don't believe in libertarian goals. To them, its just a tool. Second, they apparently believe in using force to keep two people together against at least one of their wills, a direct violation of the NAP (I mean, marriage laws even existing is beyond what government should do, but if they must exist, this is a further violation). So this person is a Christian who might be libertarian on a few issues. That is not a libertarian anymore than a pro-gun liberal is a conservative.
This person isn't a 'pure' libertarian or a 'practical' libertarian. They aren't any kind of libertarian.
Now there are Christian libertarians. They believe in the NAP because the Bible says so (I don't pretend to know the exact theology here, so I won't try to attempt it, just take that they believe it as a given). They believe that although gay sex is wrong, and so is divorce, it's up to you personally not to do these things, and it would be wrong of them to use government to stop you. Your sins that don't affect others (i.e. don't aggress on others) are your business.