>We don't do it for any other historical event. Why is that?

Sure we do, there are lots of things (usually genocides) that are considered crass or hateful to deny or downplay (let's be honest he was downplaying, he certainly wasn't suggesting the numbers were underestimated!)

I guess it comes down to this: If you're an already racist nut job and start questioning the holocaust, then I assume you're acting in bad faith and are racist. Anything else would be supremely naive, sorry, I don't have to be infinitely credulous.

And yet, there is only one event that has laws that protect it from being questioned. You said there are lots of things, but failed to mention even one.