A) Hasbro actually had to stop certain things cause the fans were making profits on their characters. Jan Animations was offering animation commissions, some people were making plushies close to the show’s designs, and Hasbro didn’t want it. So they asked them to stop, then try to gain partnerships with plushie companies so people can buy them and Hasbro gets the profits. Bullshit but that’s business.
B) Certain things are kinda bad towards the image of MLP. The reason Molestia got a C and D, rumor has it, that it was casting a negative image on Celestia, casting her not as a royal
do-nothing princess and teacher to Twilight Sparkle, but a sexually deviant tease. (NOT a rapist for those who think that.) The reason a few plushies got C and D was because they had vaginas sewed in them. For God’s sake, we’re to love ponies, not make love to them in plushie form! Unless you fuck with your cock out your fursuit or you have to wash your teddy bear frequently with a garden hose and fabric cleaning liquids, that’s not the accepted norm for this. (And let’s not go there about body pillows. I think there’s a video out there for that purpose.)
C) We love ponies but it gets difficult if Hasbro looses grip on it’s intellectual property, AKA the ponies. Copyright comes into play on this, too.
So in a sense, Hasbro had to do what it had to do, protecting it’s assets. But that doesn’t mean it’ll go after every shmuck who draws ponies. If my guess is correct, they only go after the people who make profits off show-accurate styles or will actually damage the reputation of canon characters on a large scale. If you draw or animate with a personal style, like HotDiggityDemon or my pal MofetaFromBrooklyn (an adopted Loony Toons-esque style), you’re safe, legally.