The race IQ war is never going to go anyplace good for this site, and it attracts hard-core ideologues who proceed to do hard-core ideological battle, which is off topic here.
We moderate not so much by comment as by subthread. That wasn't the only thing the parent was talking about, and there was at least one other subthread in reply that wasn't as bad. This one, however, definitely went way into classic flamewar hell. Nothing about this is going to get resolved on HN, only talking points thrown back and forth by the already-dedicated, while everyone else tunes out.