I think the short of it is that deBoer believes he has a valid point, but believes that there's is a likelihood that his intended audience will just ignore him.

I think the short of it is that deBoer believes he has a valid point, but believes that there's is a likelihood that his intended audience will just ignore him. He's trying to insulate himself from that outcome by several tactics: The elaborate denunciation of Chait, the careful choosing of targets, the stressing of his credentials and history. If deBoer could be honest, he'd probably say "WTF is wrong with you? Chait was correct, and excommunicating him for saying correct-but-uncomfortable things is fundamentally unhelpful and illiberal". But he can't say that, because the same process will excommunicate him too, so we get this instead. Not that it'll help; for some of the more extreme types, it's probably enough that Chait quoted deBoer approvingly in his article. (You'll notice that while he mouths the pro forma denunciations of Chait, he never really specifies where he thinks Chait got it wrong.)