OK, I will accept that premise, from which it follows that if the whole class skips over these parts of the material, then everyone's understanding is hurt - so what are you going to do? It seems the choices are either that we accept that certain people should avoid certain topics (which is not a controversial position when the topic is, say, mathematics) or that all potentially-disturbing topics are off-limits (at least mathematics will probably survive in that case.)

That’s correct, but you can decide to skip over parts because you value your emotional well-being more than your understanding of a subject.

As an individual, you could try plugging your ears I guess, but it would certainly be disruptive to have half the class file out of the lecture, wait for some kind of signal, and then file back in.