Steven Universe is an AMAZING show. However I do think the ratio of extremist/undesirable fans is about the same as My Little Pony, and I understand perfectly now why they openly rejected Bronies when they wanted to join in the Steven Universe fandom.
In essence, the SU fandom can be perceived as “reverse bronies”, meaning that as opposed to making a kid’s show raunchy, fetishized and offensive they are the puritans who want to preserve the entire source material in its complete integrity, making it extremely safe and inoffensive but at the same time sacrificing their dignity in order to do so.
Keep in mind that when I use this analogy I by no means think that all bronies/steven universe fans are like this. Making that statement is like saying all Muslims are Terrorists and all men are sex offenders.