Why libertarian friends make me uncomfortable

I have a libertarian buddy who is one of the more rational, clear-thinking, and honest people I have met. He keeps his word. He speaks his mind. He is always always reasonable.

I don't trust him.

The reason is outlined in this post on why taboos are important as social coordinators: (via Stumbling Tongue)

The psychology of taboo is not completely irrational. In maintaining our most precious relationships, it is not enough to say and do the right thing. We have to show that our heart is in the right place and that we don't weigh the costs and benefits of selling out those who trust us. If someone offers to buy your child or your spouse or your vote, the appropriate response is not to think it over or to ask how much. The appropriate response is to refuse even to consider the possibility. Anything less emphatic would betray the awful truth that you don't understand what it means to be a genuine parent or spouse or citizen.

This guy legitimately is my friend but I feel, perhaps unfairly, that he's a calculating friend and will stop being my friend if the price is right. Of course, anyone would probably stop being my friend if the price is right, but being open, reasoned and calculating about it somehow makes it worse.