I watched the Bronies documentary on Netflix and I got to say, I completely understand what you mean by "I would never let them by my daughter." There is something almost instinctively disturbing in the behavior of many of those men. It's like the documentary tried to shed them in a positive light but only served to emphasize the creepy undertone of the whole thing. It only left me with more questions, and an uneasiness towards the very fact of the matter.

For instance, they follow one particular young man's struggle to come out to his family. Like come out as a Brony, not a homosexual. This brings up so many questions all ready. Like, why exactly is this kid treating this obsession like an affliction of some sort? He and the other Bronies can't seem to understand that an obsession of this type, toward anything, is generally unhealthy. They perceive themselves as victims, which is odd because there's no actual evidence of any bullying or oppression of any sort. Just a bunch of people with looks of genuine concern.

Anyway, to give example, this kid decides to tell his dad...with a camera crew in tow. This guy is put on the spot and he has no idea why. The confession almost seems to come across as a confession of homosexuality. When it turns out he's confessing he's a Bronie, the Dad appears to be simply confused. He doesn't really know what My Little Pony is other than a little girl's cartoon show, and he almost seems more concerned for his son's mental well being than anything. Like the whole thing is some obscure cry for help or attention. As the doc progresses, the father goes along for the ride. He obviously wants to handle the situation very delicately. He's surrounded by cameras, he's being told how to feel and deal with his son's disturbing obsession, he's being taken through the motions one would expect needed more for a parent unaccepting of their child's sexual orientation and there's really no support for him, as though he's some sort of fairy tale antagonist. All the while the look on his face suggests to me that he's learning that his son may have serious issues. Ones which may be worse than anything he had ever mentally prepared for.

TLDR: The Bronies documentary is a goddam tragedy about a father who loses his son to the generation of victims.