He didn't bother with a serious argument, only an appeal to "causality." I don't go around posting my opinions on random threads unless I really can improve the discussion.
Most people consider causality to be a rather serious argument. If you're going to unilaterally declare certain lines of argument illegitimate, and then criticize people for failing to present a "legitimate" argument, and declaring that any opinions that disagree with you don't improve the discussion, that's probably going to piss people off,
A self-modifying AI is built to serve humanity. The builders know, of course, that this is much riskier than it seems, because its success would render their own observations extremely rare. To solve the problem, they direct the AI to create billions of simulated humanities in the hope that this will serve as a Schelling point to them, and make their own universe almost certainly simulated.
Plausible?