if you have a norm where people don't discuss certain things because it will cause offence to a group then having a discussion about things that will cause offence to that group is massive slight against that group. not only will it offend that group but it also shows that no-one cares about offending that group. i know this is a tautological argument. but i feel we do have a norm of not discussing things that will cause an offence to a group and even if you think this norm is wrong it is very difficult to change because the initial breaks in the norm are going to be resisted very heavily by those who feel they are being unfairly targeted.

Offense and harm are different things.

The problem is that they are being seen as one and the same. Words that people don't like are being seen as causing material injury. That's why professors are giving warnings before class that certain topics may be "triggering" and that students don't have to have their fragile minds assaulted by differing opinions.