The fact that it's immoral to infringe freedom of association doens't imply that it is always moral to exercise your right to freedom of association in any way

The fact that it's immoral to infringe freedom of association doens't imply that it is always moral to exercise your right to freedom of association in any way you want. We could all exercise that freedom to refuse to associate with people who are on the wrong side of the $HOT_ISSUE debate and gradually degrade the social fabric until it tears. For many possible values of $HOT_ISSUE, I think we can agree that would be wrong. So even though you aren't required to associate any more liberally than you desire--and requiring you to do so would be wrong--it's still true that we need most people to be quite liberal in their associations for this (or any) country to work. That's all a long way of saying that it's valid to complain about private censorship. It's (generally) not okay to propose that we send in the troops to stop private censorship, but it's fine and good to complain when it happens. It's no different from arguing that some{body|entity} should be nicer, or more careful, or even stricter, for that matter.