I think ignoring is an excellent tactic for a developer's list. I worry
that isn't strong enough for a user's list, but I also wouldn't want to
embark on a path that could backfire.
Not exactly the same situation as yours but one of our users went off
on one a few months back and it looked like a flame war was about to
start. Rather than flame the guy (and boy was I tempted) I found that
an extremely polite reply taking every care to be reasonable whilst
quietly pointing out where he was wrong worked very well. I actually
got half a dozen messages from other users saying something along the
lines of "Great reply. I was about to flame the <insert favourite
adjective/noun combination here> but your reply was much better." and
best of all, not a single flame in response on the users list.