Well the problem with offensive material is that people laugh because of the insults and curses. In fact that's a pretty good way of widening your audience, you can always attract people that way. But the question is, if you cut all that away, what is left? Does that stripped down material still hold a high quality or doesn't it? My problem with the "cursing comics" is that a lot of them use the cusing to cover up the deficiencies of their material.
Does offensive material have any other value? Well sure, I suppose you can find some interesting formulations. But if a comic is good at formulating points, he could do that just as well without the curses, couldn't he? Take Chris Rock, now it's not like everything he does is hilarious. And let's remember he does a lot of offensive stuff. But in his best moments, the ideas are so ingenious that they're hard to match by anyone, that's what makes him a superstar.
Billy Connolly I don't really know, I've heard half a dozen bits but nothing he did really hit me so far. He seems quite decent.