Well I think the only problem is that introduceing pokemon to the wild would throw the ecosystem out of whack, but I can't see any other problem, yes bad people would get pokemon but for every criminal there would be five more everyday good sumaritans to counter them. And plus you can kill most pokemon by just shooting them. The question of what if pokemon existed has always fascinated me, I like to think about where certain ones will live like Magmar in the volcanos in Hawaii Mew in south America, Gyrados in the Atlantic, assuming pokeballs exist I am sure they would have a Pokemon league of some sort.