The caveat there is that at the time there wasn't a invite system. You'd just add mods. So him getting modded there isn't as big a deal as one would think.
The fact that it wasn't banned until after he was long gone and only then after a CNN piece on it, that should raise an eyebrow.
Can't speak for Dorsey but Spez started out standard libertarian tech dude dumb vis a vis making reddit "free speech" and enabling the jailbait and racism subs to exist.