That may be true (not at any sci-fi con I've been too, but I admit my sample is not large or North American), but I would also not expect to see explicit sexual behaviour (and I'm sorry, feeling up someone's tits is) in that kind of public context. I agree that fetishwear can be confronting, but if you're expecting it, fine. Most cons do have a well-known culture of "dressing up".

But if there is going to be sexual behaviour, I'd rather be prepared for it. I attended a poly conference which happened to have no overt sexual behaviour, but it would have been fine if there were (up to a point). I would simply have gone elsewhere if something had started up that I wasn't willing to be a party to.

That was something I was prepared for, not a bunch of geeks deciding something amongst themselves, and then perhaps attempting to normalise that behaviour in that context - it can be very difficult for some people to assert themselves against certain kinds of peer pressure (although I'd agree that it's useful if people do learn to grow a pair and tell the breast-feelers to fuck off and find a room).