Wasn't sure if you put this here or in the film, tv page, but figured its general enough to go here.
Speaking as a 33 year old dude who when he was a kid did watch the original my little pony cartoon series, since then I forgot mostly about that and grew up loving x-men, batman, computer games and all the usual stuff.
I never even pegged my interest when seeing my little pony stuff still produced years later, including when the current generation of it became popular, and so of course I wondered what this whole brony thing was based around any why it existed.
So having watched some of the episodes of MLP-FIM, my overall opinion is that its a good show, and a lot more well written then any of its previous series, I've also watched some youtubers applying critical analysis of the episodes and like some of the reviews. But again, I've not become a fan and while thinking its a good show, its not something I'd get into watching as a habit.
So on that end it made me wonder just why is there such a following for adult men, bronies, to get behind it. At best what I can take a stab at, is some men saw the show, and liked it, the story, the character design, the overall premise of the series, and became a fan. They told others they liked the show, and got given some negative feedback by them, which resulted in them forming a cultural following for men who felt the same, and formed a fandom around that, made even stronger when it got ridiculed by people like online.
At least thats my thought on it. maybe I'm wrong.
My overall thought on bronies and the haters is while I think MLP-FIM is a good show, and can understand it having a following, its always struck me as a little extreme to form a cultural fanbase around it for grown up men, not to say that its a bad thing, just that given this show came from a long line that had always been advertised for little girls, yeah, you can see why people would argue it being just for little girls and why they find it strange.
But then against the haters, does it really bother people so much that adult men like a decently written cartoon series? I think MLP has better writing then most of the other cartoons out now, so there is no wrong is liking the series. I just couldn't become a brony in the militant sense as others have. Its kind of like, speaking as a gay guy, if someone came up to me and laughed say 'haha your a cock sucker', I'd just smile and say yeah, yeah I am, you should try it one time.