That's like saying the extensive campaign to prove the earth is a sphere proves it's flat. That isn't how logic works.
First they make you drink fluoridated dihydrogen monoxide, then when you get a job in enterprise IT, the extra ions in your teeth make you pay extra for vPro.
Conversely, if ME/PSP actually is a hardware backdoor:
1. The proprietor of the backdoor would've expended considerable resources designing, implementing, testing, and distributing it, and thus would have an economic incentive not to see it exposed and discarded so as not to incur development expenses on a successor.
2. The proprietor of the backdoor would have an operational incentive to not have collection disrupted by the backdoor being detected, exposed, and discarded.
Your comparison of what looks like a real conspiracy to a known character-assasination conspiracy (flat earth) is consistent with COINTELPRO techniques.
I'm not accusing you of being a bad-faith actor, but you're arguing against someone who is opposed to an alleged US intelligence agency backdoor, using rhetoric consistent with known techniques used by US intelligence agencies to disrupt conversations (and discredit participants) who are exposing US secrets.
Then they should use better arguments and not "everyone saying one thing somehow proves the opposite".