Two words. Very simple.
Which part of it exactly is it that people do not understand?
On a social/political/discursive/philosophical level, being offended means absolutely nothing. It bears no significance, and it most certainly has no value whatsoever. The only time when someone being offended is important is in a personal relationship, where the feelings of the other person matter and respecting them actually serves the purpose of the relationship becoming healthier and more intimate.
More than any other manifestation of free speech, comedy is the one that can (and must) talk about anything it damn well pleases, and it is also a medium that goes dark places. It shines light into the dark, and it makes hard things soft. It distances us from the absurdity of the world’s tragedies, and it allows us to draw both wisdom and entertainment out of them.
Rape jokes are OK. Jokes about death are OK. Jokes about racism are OK. Jokes about murder are OK. Jokes about anything disgusting, vile, visceral, dark, depraved and taboo are -you guessed it!- O-FUCKING-K.
Nobody cares if you don’t like that or if you can’t wrap your tiny head around this matter. Read some of this (especially the last few paragraphs) and maybe you’ll start getting it.