No. They are only guaranteed a say in discussions that they initiate (by posting them). That's the way it works around here. I can start a discussion, and I can exclude you if I like. Tough shit for you.
If you've pissed off someone and they mute you, buck up and roll with it. Or ask to be un-muted (politely, I'd suggest). But you do not have a right to comment wherever you want around here.Because they're allowed as much a say in the discussion as anyone else.
As much as it might hurt to be quietly muted by people you once thought were your friends, it is true, nobody is guaranteed a say on any post that isn't their own. I'm the biggest advocate of "freeze peach" as there is, but even I can recognize that this is how Hubski works, and it isn't that bad, especially if we're comparing it with the more draconian and top-down version of reddit moderation. Say what you want, and if you can't say it in a reply to someone, then say it on your own. If it's that important, and you're civil, I take an optimistic view that you'll still find an audience for your opinions. And if not, well, the world's going to hell in a handbasket anyways, so what?