The question itself is questionable. Everyone has free rein, and everyone has the right to be offended.
I would agree with this position, but only add that, as in all things, THERE ARE LIMITS. This is the paradoxical truth, especially in a society like ours where we value free speech. I don't think that anyone here thinks that the governments of any kind should censor through their powers the subject matter of a comedian's act. That most people think would be a violation of another person's freedom of speech, and I would agree. But is that really the question here, or when this subject usually comes up? No. I think this is about things that rightly so are beyond any government's power. It's really about questions of taste and self censorship. In a free society, sure, comedians have the right to offend. As pointed out though, people can "vote" as it were with their dollars and private entities of every kind that would matter to a comedian's career (clubs, broadcast/cable/Internet platforms ect. ) have their own rights not to employ or showcase that comedian if they so choose.
Comedian Jeff Garlin spoke about this once in a New York Times Magazine Interview (I'm choosing Garlin, as a comedian's comedian to site since I am sure someone is going to quote Carlin and point to him as the final word on this for all comediens, and that's just not true... Carlin's position is not EVERY comedien's' position). His position was that comedian's sometimes forget that they are in a dialog with the audience, that the audience in fact exists at all.
Garlin thinks, yes, a comedian has the right to make, say, a rape joke, but that doesn't mean they have some immunity in a free society from catching hell about it in some way (as long as the government doesn't get involved). People have a right to be offended as much as the comedian has his right to possibly offend.
Now, the audiences reaction also has limits as well. If someone is saying something you don't like, well, make your opinion heard, fine. Vote with your dollars, as was mentioned. Protest. Boycott. All to my mind perfectly acceptable, and it can have an effect. A broadcaster makes offending remarks and people make a stink which makes the network think it would be best if he worked elsewhere? Welp, them's the breaks. No one is violating his right to free speech. He can still say what he wants (more than ever in an Internet age) but he doesn't have a RIGHT for someone to give him a platform for his speech, what ever it's merits. The owners of said platform have their own legal and indeed personal rights as well. These can be the results of what let's call, valid offense, or at least what I think is a valid response to offense of all stripes. What is not valid is the aformentioned actions by the government, but also the acts of individuals and groups that cross the line into violent action in an attempt to intimidate anyone or anything into silence.
Look... There are many comedians I just don't like. I call them on their offensiveness when I discuss them with others and let my opinion be heard. As a human being I think it's a mark of maturity and wisdom to on my own part to self censor my own speech for a wide variety of reasons, and I bet there are tons of comedien's that do the same just because they feel similarly, they would feel bad about making un-ironic remarks that are flat out offensive or don't want to face the consequences of their saying something they know is going to be offensive. The hard and fast rules usually melt away under the sunlight of real life practicality when an issue like this comes up. Yes, comediens have a right to offend, but like it or not, there are limits (if people choose not to support said comedien financially, guess what? That's a limit). People have a right to be offended, but again, there are limits.
This is indeed where, beyond law, and other rules, the quality of WISDOM comes into play, but it seems when stuff like this comes up many of us want black/white, hard and fast rules, and hopefully, if you've lived long enough, you'll have acquired the knowledge and experience to understand, that's just not how life is for the human animal.
