Well, even if you completely trust Intel to never be nefarious, never act against your best interest, never do anything shady whatsoever with that power, you can't trust them to keep that power only for their own use. This vulnerability is proof of that.

So you don't have to claim that Intel could have bad faith. You can claim, with proof, that Intel has less than perfect success at security, and that less than perfect security is reason enough why this "secret computer inside" is a horrible idea.