The difference, in what we in the cheap seats can do, is between saying, "Harlan Ellison is nasty! We hate Harlan Ellison!" and saying, "Please do not invite Harlan Ellison to be any part of presentations at this function in the future. The knowledge that Harlan Ellison was going to be on stage would make me less likely to attend or publicize any event."
yup, that would be one way to handle it. i feel a bit torn about that sort of action even though i participate in it at times -- boycott is a double-edged, heavy-handed sword. i tend to reserve it for a point much further down in the "teach people to behave in a civilized manner" course. (also, FWIW, ellison has said this will have been his last con, so the action's effectiveness is in question.)
i would prefer to start with writing a letter of censure to harlan ellison, and have it signed by many of those who agree that this type of behaviour is unacceptable. or start a letter writing campaign, so people can express it more personally. i like my justice to be direct.
but either way would be better than merely exchanging anecdotes of other nasty ellison incidents, or bringing up how asimov did bad things in his career too as somebody in my LJ did. *rolls eyes*.