Thomas Shey
Legend
There is, of course, slightly more to mind flayers than simple diet though. Mind Flayers enslave other races, even those they don't eat. Now, while you can argue that they have to eat intelligent beings, the torture, slavery and various other ickiness is kinda a damning point. It's not like they absolutely have to enslave intelligent beings to do their bidding.
You can make the argument that the enslavement, unlike the consumption of intelligent beings, is a social thing and says more about mind flayer society than mind flayers, however; if you got a philosophical revolution, they could knock the slavery off.