Without a doubt - she goes well beyond the bounds of good taste - but so does Louis C.K. - who is considered the foremost comedian of our (current) time.
I don't find Louis funny 90% of the time. Once in awhile he hits on a gem, but when he decides to go crude for laughs, sadly, it wasn't worth going there.
If I am going to lower my moral compass for a comedian, it had better be funny. Joan is truly funny (and crude), Louis CK, is just crude when he attempts to go there - and I do get offended.
That is the thing about comedy - if it makes you really laugh it is justified. But what I really resent are people who do "jokes" in the name of comedy that really are not jokes at all, they are political rants.
I can enjoy political comedy if a joke is funny, but take someone like Bill Mahr who will make a joke about Sarah Palin being stupid, (and by "joke" I mean its a fictional story) and he expects you to think it is funny not because the joke is good, but because its about Sarah Palin, then I am offended.
But I would rather hear that joke from Joan Rivers than listen to Bill Mahr's audience laugh just because he says "Republicans are A*****es." (and they will surely laugh, because they actually think that is comedy.)