One standard reply to this sort of thing is that people may be reading the thread other than the people replying to it and the Monster Raving Loony who started it. Let’s face it, many people–most people–are probably pretty ignorant about a great many things. They believe the Holocaust happened for the same reason they believe the War of 1812 happened, or that there’s a country called Nepal somewhere in Asia–they learned about it from a book back in high school.
Now, along comes some guy who says the so-called War of 1812 is a big fat lie, or there’s not really any such place as “Nepal”, and he reels off all sorts of statistics and very practiced arguments allegedly debuking the nefarious Nepal Conspiracy. Well, how the hell are they supposed to know what’s true or not?
So, we post facts and arguments (in between truly massive amounts of snark) because supposedly this place is or will soon be indexed by Google, and you never know who might wander in here–maybe even someone who has run across one of these guys and is thinking “Damn, that can’t be right, can it? I mean, old Mrs. Wormwood, my high school history teacher, said there was a war in 1812/country called Nepal/deliberate mass murder of the Jews by Nazi Germany during World War II. Old Mrs. Wormwood wouldn’t have lied to me, would she?” and so they Googled “Holocaust hoax” and out we popped as link #12,742.
Also, hard-core deniers may be unlikely to see the error of their ways barring the discovery and succesful removal of a brain tumor; but I believe there have been cases of naive people who’ve been roped in and then later changed their minds (see Jean-Claude Pressac). Again, who knows who all could be reading that thread (or any other public argument on the subject); maybe someone who’s lurking and saying “Yeah, that’s right! Give those Holohoaxers what for! You tell 'em…Huh, I’d never heard that before. That–that can’t be right, can it?” Not right away of course, but cumulatively, perhaps simply from having the same old lies shot down and the same old facts presented over and over again, with new presentations.