The onus should not lie with the offended party to just not be offended, it should lie with people trying to not be offensive.

Jesus, I didn't really want to respond to you in another thread but this line I had to say something. Anyone can be offended by anything, so you're saying everyone should go out of their way to not offend anyone? Ok I'm offended by your user name, change it. I'm offended by the way you speak, the onus is on you to change it. I mean a society with that mindset wouldn't function, anything I didn't like I would just say it offends me and demand you change. We need to follow laws, that's why we have them, and we should strive to be good people, but suggesting that a person should try to conform to every little offense anyone could have is unreasonable, that's a VERY slippery slope.

No amount of perspective will get me to react kindly to statements like “women belong in the kitchen”.

Unless you live in a world where that is normal for decades on end and it becomes your normal. Nazis never saw themselves burning people in ovens, it's not a switch that happens over night. What can become your normal is very scary.

What narrative is furthered by feeling something?

For example saying that you are offended by pride flags because you are homophobic. Maybe you "feel" (general "you", not you specifically) that gay people touch kids, many homophobic people do "feel" that. Feeling that way and expressing your offense to pride flags in that way very much is pushing a homophobic narrative that can be damaging to the gay community.

Being offended doesn’t protect you whatsoever

That's not what defense mechanisms are in psychology. They are subconscious responses, usually to avoid anxiety or facing any cognitive dissonance. If you point out that they hate gay people but are best friends with a gay guy, they may get offended as a way to avoid confronting that cognitive dissonance.