> Functional markets require a strong mechanism for protection of property rights. The fact that we have some historical systems where that has taken a different form than a conventional government doesn't negate that the only practical mechanism that we have to protect property rights and support markets is a government.

Even if we grant that argument, that's at most an argument in favour of a minimalist nightwatchmen state. Not the full blown Leviathan.

> And then, there's lots of situations where externalities exist. If I poop in the river and you're downstream, it costs me nothing; I have no reason to stop.

See https://en.wikipedia.org/wiki/Coase_theorem