I've seen, several places, people saying that This Is Going To Be Harlan's Last Con and thus there's no point in fandom itself dealing with it via banning him from a con or what have you. (As opposed to any legal actions that might occur, although I hasten to add that I haven't heard of any possible legal action and don't anticipate it happening.)
I'm certainly not sitting there going, "Yeah, let's lynch him!" because I /wasn't/ there and don't know details, but given what Rachel's said and given what he himself said about his actions at the awards, I don't see that fandom (or, rather, parts of fandom) enforcing consequences in a con context is useless. It would be a positive action taken by whatever portion of fandom chose to do so, and even if he never goes to another con (or, anyway, another World Con, whatever), it would still indicate that whatever portion of fandom acted in such a way means what it says, in terms of what it does and does not allow and welcome. And a consequence is still a consequence.
(I put the disclaimer that I'm not active in fandom all that much, except insofar as occasionally going to Boston-area Cons, so I am to some extent just talking out of my hat. But I mean well...?)