Accepting for the moment that our stated principles are okay (which is where I expect you might disagree)

This is not a good thing to accept, since the stated principals are themselves subject to change. Hence

5. Once society starts taking complaint X seriously enough to punish the perpetrator, people start making (weaker) complaint X'. Once society takes that complaint seriously people start making complaint X'', etc.

I would argue that long term 5. is actually the biggest problem.