but even a sysadmin at a fortune 500 company is in the dark about all that this second cpu can and can't do.
The sysadmin might not know how it works, but they do know they can control machines remotely using their Intel branded management system (or other rebranded variety). Just because they don't know how bad it is doesn't mean that's not the motivation for it.
IPMI is a similar deal. Modern servers have a secondary computer embedded in the motherboard (which have been historically _very_ insecure) because it's useful for managing servers. Intel AMT is the work-laptop version of that technology, and you can bet that most enterprises use it.
> if it was economical they would offer you to pay more for full control for it.
But they do. The entire reason why enterprise deployments of large numbers of work laptops/desktops is so expensive is because you have to pay extra for the management system that comes with it. Just because they don't remove the "backdoor" in their consumer lines doesn't mean they won't charge you through the nose to be able to administer the damn thing.
I am very anti-ME and wish that all firmware was free software, but arguing that the reason why ME is present in consumer CPUs is not for economic reasons doesn't sound right to me. The reason why the technology was developed is because the developers were not aware how unethical their actions were, and that's where the core of this problem lies.