You can't change the boot media or turn on a turned-off machine via the OS. The whole point is to get underneath it, so you can even do initial OS install with it.
It might not be trivial, but you can do this w/o the ME. My understanding is that most ethernet cards support a "Wake-on-LAN" feature to turn off machines on, and from there you can trigger the machine to reboot and then netboot (by writing to its boot config to instruct whatever boots it that it should take that action).
Even if you assert that the ME is absolutely necessary for such a use-case, I don't have that use case, it isn't work the risk for me, and I should be able to disable the ME because I, as the owner of the machine, want to. (Or really, otherwise interact with it and use it for creative use-cases.)
That disqualifies a lot of otherwise really good hardware. My current Thinkpad, for example, and all current MBPs, I believe. Some manufacturers also aren't very clear about the exact hardware in their machines, either. (For example, Apple doesn't list the exact CPU on their tech specs page, only the somewhat vague "2.4GHz dual-core Intel Core i7, Turbo Boost up to 3.4GHz, with 4MB shared L3 cache". That might be unambiguous enough to map back to an actual piece of hardware, but it's still a considerable amount of work to do so.)
Even if you assert that the ME is absolutely necessary for such a use-case, I don't have that use case, it isn't work the risk for me, and I should be able to disable the ME because I, as the owner of the machine, want to. (Or really, otherwise interact with it and use it for creative use-cases.)