A lot of the pushback against conferences adopting an anti-harassment policy has been in the form of grousing about evidence (or lack thereof). Obviously we know this can be a problem, as these sorts of situations can easily degenerate into he-said/she-said.
But I think this is ignoring a lot of low-hanging fruit, if you'll excuse my use of what may be a somewhat tired metaphor. The assumption seems to be that the typical serial harasser will repeatedly deny everything and, as long as there are no tangible consequences, continue his behavior without modification. While it's undoubtedly true that there are people out there like that, I think this is the exception rather than the rule.
I think people will be pleasantly surprised how much of the more egregious behaviors decline precipitously as soon as there is a procedure in place so that conference organizers can have a chat with an accused harasser and merely let him know that the behavior in question is unacceptable. Sure, there will be those who laugh it off. But even just establishing that there are boundaries and that there might be consequences eventually is often enough to induce someone to change their outward behavior, at least in that particular context.