The Thing is, the 9/11 Joke is unfunny, but not because it´s offensive but because they just bring up 9/11 without making a real Joke. He should have criticized the lazy Writing instead of "HOW DARE YOU MAKE A JOKE DON`T YOU KNOW THAT FIFTY BAJILLION PEOPLE DIED". And honestly, I have heard more offensive Jokes in an ifunny Comment Section
The issue with "offensive" "humor" is it's usually either done by children that watched two episodes of South Park/Family Guy or it's done to strongarm another person's (usually short-sighted) world views. Both instances are lacking.
Offensive humor is funny, lazy humor isn't. The difference between the two comes down to just saying a naughty word vs. saying naughty word with actual nuance and a point.