While I like (and agree with) the advice given, and especially Ryan's excellent example, I will say that it is possible to keep snakes together, and even different (though obviously with similar requirements) species in some cases. However, there are some disadvantages at the best of times, and the potential for disaster is high if you don't know what you're doing. I don't advocate it in most cases, though I do it myself.
Oh yeah- cannibalistic tendencies in kings and milks, certainly. With corns? Not very likely. Certainly not in my experience, keeping various corns together for the last 8-10 years.