YC is one of a small number of organizations who can write something as simple as this and have this impact, because VCs compete for their dealflow. It's not the writing itself, so much as the realization that they could have this impact by writing it.

It's very simple, straightforward and unambiguous. No-one will be able to say "oh, I didn't realise" afterwards.

Nobody can reasonably say 'I didn't realize' now. This is not a new 'trend.' This shit has been technically unacceptable for a while.

And just as technically it has been unacceptable in practice that won't change anything.

People modify their behaviour depending on the consequences they reasonably expect. For all that some harassers say that their behaviour is normal or unintentional, they don't really harass up the power hierarchy. That's actually quite a good litmus test.