While I am definitely of the "fool and his money" way of doing things, I can see why Mojang feels the need to kill or damper "pay to X" servers. No doubt they've received lots of angry calls and letters from players who feel cheated, from parents who don't understand how their kid racked up these costs, et al. It damages their brand, and telling people "that's your fault" doesn't usually go over well.
However their response seems a bit heavy handed, considering how other companies have handled stuff like that. Halo seems to me a prime example--if you want, you can basically do anything. They've highlighted fan comics on their website, hosted game shows created in Halo: Reach, et al. They don't really approve of modded content, but unless you're trying to cheat in matchmaking they don't really do much--even Bungie before them would ban you if you had modded content in your fileshare. The only condition is that you don't sell it to make money--and even that is open to wiggle room; there have been a lot of Halo-related kickstarters for fan films, etc., where since money was going into production and it was clear it wasn't an official Microsoft project, they stayed clear and gave the okay. Why doesn't Mojang just do this? If they're concerned with how paying servers are corroding the experience, then they probably should focus more narrowly on that.