Assume we could have two planets in an overcrowded universe. One that has reached its carrying capacity, one that hasn't. By chance, you could wipe out the underpopulated planet and some few other races to make up the "half" that is wiped out, and by chance leave the overpopulated planet untouched? Isn't that, oh I dunno, retarded?
Also Thanos's plan excludes himself. He wipes out half of the universe knowing full well that one day the universe will be populated back to that same point, therefore somebody righteous enough will have to take on that Godly role. In other words, even his "randomly selected without prejudice for class" concept isn't true, since he's the highest form of elite that is beyond that fate.
Or he could even increase the universe's resources with his god glove, or simply make half of a universe infertile. Whatever he does will have horrible ramifications, but specifically killing half of them is just dumb. His plan is poorly thought out, which would fit his obsessed-with-death personality more than his 200 IQ sympathetic villain characterization in the MCU