I looked through a couple of the threads.
1) The arguments you use aren't austrian. You sound like a Chicagoan. This works to his advantage because he is attacking the Chicago/Neoclassical school. You aren't running praxeology, the incentive problem, the calculation problem, or anything of the sort (in what I read). Don't let him frame the debate. For example, when he talks about how human beings aren't rational you should just perm this under praxeology and continue with the incentive problem.
2) Bone up on subversive politics. He only speaks theoretically about the welfare state. The minimum wage law was originally passed by white unions to stop blacks and women from competing and taking their jobs. How can a law that was intended to be bad for minorities be good for them 50 years later?
You have history and data on your side as an Austrian and as an Anarchist. You can open up Pandora's box on him for any issue, from economics, to justice, to war. Whatever problems someone sees in society, the establishment of a monopoly legal system is a non sequitur.
3) Work from a coherent anarchist framework. Usually once I explain this to people they realize their position is completely shot.
Definition: Anarchy: When there is no one third party to resolve disputes between people
The State of Nature: A dispute arises, and there is no judge at all to resolve the case. Chaos ensues.
Government: A dispute arises, the state handles it. The incentive problem inhibits the state's ability to resolve disputes between citizens properly. However, for disputes between individuals and the state, the state is the judge and we are in Anarchy again because there is no one third party arbiter. The state is judge in its own case. You can see how this can be worse than the State of Nature, because the state knows in advance its going to win all of its cases and will behave accordingly.
The Ideal situation: For every conflict, there are numerous competing third parties one can appeal to. Rothbard and others have written extensively on this subject and you should read up on PDAs/DROs etc etc. There are many threads and articles about this. But to defend the position negatively there is no way it could ever be worse than either of the two scenarios above. For in its worst case, we simply devolve into the State of Nature.
You never have to lose an argument because you are honest and they are not. We are practically the only school of thought without a conflict of interest. Liberals want to be PC. Its part of their self identity. Republicans want to seem macho etc etc. None of us here on these forums benefit our self image from being AnCaps, and we particularly do not benefit personally as open borders and free trade would reduce our inflated standards of living at least temporarily.