First, there is too much capital chasing too few opportunities today. Y Combinator is widely seen by many investors as being the highest-quality accelerator so if it had merely stated "Y Combinator will not tolerate inappropriate sexual or romantic behavior from investors toward founders. Period." I guarantee you it's not going to suffer any negative consequences. I'm sure there are more investors wanting to attend Demo Day than there are Demo Day invitations.
Second, Y Combinator could have prepared a code of conduct and sent it directly to the investors invited to participate in Demo Day. Demo Day is an invitation-only event and sending a code of conduct to invitees via email would have been a more effective way to reach the target audience than publishing a "Reminder to Investors" blog post which was clearly intended to be read by a broader audience.
I don't doubt that Y Combinator sincerely wants to quell this behavior, which is a good thing. But maximizing the good you do isn't always aligned with maximizing the PR you do.
Second, Y Combinator could have prepared a code of conduct and sent it directly to the investors invited to participate in Demo Day. Demo Day is an invitation-only event and sending a code of conduct to invitees via email would have been a more effective way to reach the target audience than publishing a "Reminder to Investors" blog post which was clearly intended to be read by a broader audience.
I don't doubt that Y Combinator sincerely wants to quell this behavior, which is a good thing. But maximizing the good you do isn't always aligned with maximizing the PR you do.