Telling people to go away makes them stop listening to you - and probably not "go away", but "find people who agree with them and hang out there instead".

Yeah, I see this in the wild pretty often and it seems... suboptimal. Not to name names, but when you get lots of creepy-labeled people hanging out together, one natural consequence is the formation of identity groups based partly around the behaviors that got them labeled as creepy in the first place. Which in turn creates positive reinforcement that makes those behaviors a lot harder to get rid of and the process of removing them a lot more painful.

That seems like a straightforward loss for everyone, except in the hypothetical case where allegedly creepy behavior is consequentially positive but maintains negative associations thanks to some random social hangover -- and I think those cases are pretty rare.

I suspect you and Matt are talking past each other a bit.

Let's say we've got a guy who went to engineering school, works as an engineer, and plays Magic the Gathering in his spare time. As a result most of the people he has interacted with over the past decade are men, and evolution has programmed him to feel desperate and act creepy. Is there any ethical way for him to overcome his creepiness problem? Matt's arguing that maybe there isn't, because even if he finds women to hang out with, he'll end up creeping them out some at first by accident. So the ethical thing to do is to avoid women at all costs.

What's your take on this argument? My take is that someone needs to give Matt a big hug.

not "go away", but "find people who agree with them and hang out there instead"

I'm not sure what the difference supposed to be. If they hang out with someone else, and are happy there, and don't bother you anymore, how is that "not going away", and why is that not a good solution?

The problem seems to be not your scenario, but the one where they fail to find people who agree with them and hang out there.

ETA: reading Nornagest's comment below, maybe you mean that they find others who agree with them, but instead of hanging out together somewhere else, they come back with those others and bother you as a group (or bother someone else). That's a problem, but if these other similar-minded people are around to be found, I'm not sure if not telling them to go away will prevent them from finding one another and banding together.

Tl;dr of my point: telling people to go away should on balance make them go away more.

Yes, but I'm not so much interested (right now) in what are the optimal rules to impose on people; I'm asking what is the right thing to do, which is a subtly different question. Your argument that eviction leads to problems in other places is clearly true. Analogously, it would be a very bad idea to impose a 80% marginal tax rate on top earners to fund the Against Malaria Foundation, because most of them would work less and there would be huge deadweight loss. However, Peter Singer and people like that argue persuasively that very wealthy people should as a matter of principle voluntarily give a high percentage of their income to efficient charity. And this causes no deadweight loss if they make sure to work as much as before.

Similarly, if there are creeps in your group, don't you wish they would just leave, and not try to infiltrate another innocent group? Then that is what they should do.