I have mixed feelings on ME tbh. It shouldn’t be in consumer grade hardware at all, but it definitely has applications in enterprise environments as far as device management goes. Having an out of band solution that runs independently of a given OS on your devices is handy.
But without someone forcing that, for consumer hardware they will just "disable" (read: not mention) the ME, because there are entities (the ones that should be enforcing secure consumer hardware) that very much enjoy the ME being there for them to take advantage of on consumer hardware.
Because parts of it have already been reverse engineered, we know it runs a modified version of Minix, and I would think that if a backdoor had been found during the reverse engineering process, that it would have been huge fucking computer security news.
It's only a backdoor in the sense that Intel was practicing security through obscurity instead of real security. There is proof an attacker could abuse the IME, but there is not proof it's an intended backdoor for use by Intel in spying on their customers.
EDIT: Further, as an all-AMD user, I almost never see this same scrutiny applied to the AMD Platform Security Processor. We know far less about it, and it deserves the same level of scrutiny, honestly.