and how many of Cao Cao's generals turned on him for it? How much of a deal did history make of it? How many of his opponents used it as evidence of Cao Cao being evil? How many scholars complained??
Possibly because Cao Cao had now turned into the most powerful man in China. It would of been stupid for any of his Generals to turn on their own Lord. It's like a dog biting his owners hand he feeds him with. Personally I believe most 3K Officers would drool at the opportunity of recruiting 10k seasoned soldiers in basically an instant. It is pretty easy to imagine a officer would be pee'd off at a order to execute all of they men, even if the officer understood why.
I said what I said because there are many examples through out history of Officers strongly disagreeing with rulers, even if it is in a personal journal or to the mouth to their loved one. It doesn't need to be one of action.
So if Cao Cao's going to hell for it, is nearly everybody else in 3k China?
Quite possibly.

But honestly maybe I shouldn't of said that. That could start a massive debate.
Cao Cao was not stupid enough to reject extra troops if he could have them but he didn't have the supplies
True. But I think he could of been possible gain more supplies. If Cao Cao was comfortable about mass execution. I can't see why he couldn't send 50 - 100 horsed men to conduct raids on Yuan Shao's villages/ towns and these places wouldn't of been well defended, Cao Cao did now have to momentum... Why not?