Controversy??? Where?
Basically, the issue is that it isn't the *best* choice for hunting deer. It takes 900ft lbs and proper placement to humanely kill a deer. The 7.62x39 is right around 1500ft lbs.
It's a case of "magnum-itis" as I like to call it. By today's standards, that 1500ft lbs is pretty anemic. Nevermind that the previous generations of hunters used ballistically similar rounds without any problems.
Besides, isn't this what we're here for? It'd be pretty boring if we all agreed with each other...