If we accept that any one person can take responsibility for their feelings then it follows that everyone is responsible for their own mind. Otherwise what exactly are we saying? And emotions are complex, especially offence, it is practically impossible to say that something will reliably offend a specific person without trying it and seeing how they react. Even for the reactee. Someone can easily say "whatever happens I won't get offended". But they might get offended anyway and then we're rolling the dice on whether they are vindictive enough to hold a grudge.

People learn that lesson then don't stir the pot without reason. Rather than saying "I don't get offended" it is generally better to prove it and push people for feedback from time to time.

There is also a subtle point here in things like "if the design is wrong, say it is wrong" - how is someone supposed to know if the design is "wrong"? Philosophically it isn't possible for a design to be wrong, the idea is nonsense. Designs have trade-offs and people might or might not like the trade offs. But a design can't be wrong because that implies there was already a right solution that people could deploy. If someone is going to be direct that is also a problem they run in to constantly - they're going to be directly saying things that are harsh and garbled. A lot of humans aren't comfortable being that person, there is a more comfortable style of being clear about observations, guarded about making value judgements from them and associating with like-minded people from the get-go rather than pushing to resolve differences. And spending a lot of time playing social games to work out how to organise all that.