Saying "humour is subjective" does not make crap like the Shatner roast funny.
I have absolutely no problem with comedy that involves horrendous vulgarity so long as it's COMEDY not a bunch of juvenile nonsense that uses rude words as a crutch in lieu of anything that's actually funny.
Richard Pryor, George Carlin, Eddie Murphy (back in the day), Billy Connolly Chris Rock, Eddie Izzard, Robin Williams; these are all hilariously funny stand-ups who's acts typically consisted of a LOT of vulgarity, but the vulgarity wasn't the reason they were funny. At least not the sole reason and certainly not the main reason...that is assuming you have an IQ greater than a concussed budgerigar who's lost his little mirror.
They were funny because they are (or in some cases, were) sharp, insightful, intelligent and entertaining. Take all that away and you're left with a bunch of idiots spewing obscenities, which is what I saw at the Shatner roast. That and some issues that George bless him should have really been discussing with his therapist. Bill may have been a complete cock to him 40 years ago but bloody hell, get over it man!
I agree with most of that. I like some insight and intelligence with my comedy as much as the next guy. I also think the Roasts are funny because they're explicitly not about being insightful or intelligent. It's different than when a dumbass like Larry the Cable Guy (who ironically had a Roast) is crude for the sake of it because he and his audience aren't in on the joke.
Those comedians know they're pushing it just for the sake of it and it's being done with a wink. I don't know if you've seen The Aristocrats but that's a perfect example. It's an anti-joke. It's funny because it's so flagrantly crude and not funny.