Actually I think yters deals with your sort of complaint. He deals with it fatalistically. Libertarians will continue to say that libertarianism never had a clear shot. Communists will continue to say the same. Both are not particularly easy to test. This argument is stuck when you encounter this.

But we do have a situation that is not high level theory that we need to make a decision about: We can push Governments to be more/less liberation, elect libertarian politicians etc. etc. What are the likely consequences of these actions assuming that an imperfect world exists where there will be opposition from politicians of different opinions etc.