Mojang does not have to allow players to make servers at all. They dont sell that ability, they allow that ability. To be completely honest Mojang allowing players to play on servers that the player creates without playing mojang any money is the same as blizzard allowing players to play on private world of Warcraft servers without them paying blizzard. Mojang could monetize the living hell out of this game, and the fact that they haven't should be something players thank them for every day. Your privately ran server is something mojang allows to happen, but dont have to. Every server should have to pay Mojang to be allowed to be played by players.

All I am saying is that if you are going to have a game where kids are involved, moderation is required. And as a company that moderation cannot be allowed to be left up to the players.