The limitations that you suggest exist within Libertarian/libertarian doctrine to the absolute right to contract seem to be in conflict with the necessary consequences of the philosophy. The individuals in that thread seem to me to be taking the "pure" libertarian position.
Not at all. Obviously, individuals may act unwisely and to their ultimate disadvantage. Nothing in this world is perfect. But it is difficult to imagine a scenario in which an individual, unconstrained by coercion and in full possession of her wits, would voluntarily agree to bind herself to abolute, unquestioned service to another for life. In return for what?
Clever use of sophistry can often serve to entangle one's opponents in endless, circular, and fruitless discussions, but this may also be done with "Republican" or "Democrat" doctrine. The real question is, which aspects of a philosophical viewpoint are likely to be useful in the real world? I submit that an unfettered individual right to enter freely into contracts fits better with our vision of a free society than does constant and intrusive scrutiny and second-guessing in these individual decisions by governments. (Governments are, after all, composed of human individuals who cannot be presumed to possess superior knowledge of the particular circumstances than the individuals who propose to enter into a contract, committing their own energy and resources to the matter at hand.)