Also, collective action problems. I haven't yet seen a libertarian who can convincingly address them. Either they simply haven't taken them into account (which

Also, collective action problems. I haven't yet seen a libertarian who can convincingly address them. Either they simply haven't taken them into account (which is the danger of relying too heavily on old texts like Smith, or even more recent stuff like Rand and Nozick), or they take a hard line stance on negative rights that suggests they care more about protecting their ideological commitments than addressing the problem.