In my opinion, once I claim a right for myself, it then extends to others, because I must live by the standard I set for myself, in short, the golden rule. If, as a society, we share a common tradition of respecting certain rights, then they exist for us. That is the point of political discourse, to establish what rights we are entitled to and what limitations, if any, should be put on their exercise. To my mind, a right is absolute, but once you violate someone else's rights, you've forfeited for yourself the rights you've violated, in a sense, by your action you're asserting that those rights don't exist for them or yourself. Ian was right, insofar as you'l only have the rights you claim and defend, and you extend those rights to others regardless of whether they believe in them. So, what he was getting at when he was saying to Mark that even if rights don't exist in a tangible sense, when they are violated by people who neither believe in nor respect them, it is still wrong because he, Ian, and everyone else who DOES believe in and respect them recognize the violation.
It was J.S. Mill who said, "If all mankind minus one were of one opinion, and only one person were of the contrary opinion, mankind would be no more justified in silencing that one person, than he, if he had the power, would be justified in silencing mankind." I agree. But there is a certain irony in that fact that a thoroughly individualist philosophy like libertarianism requires a community of like minded persons for it's existence. Man, I hope I can convince my wife to move to New Hampshire!