It's a show for little girls, but it's also written and produced by the same woman who wrote and produced Fosters Home for Imaginary friends. I'm not really too fond of the show, but I can actually sort of see why people other than little girls watch it.
As for people obsessing over it, eh, it seems to me to be more of a sort of novelty in being able to say "I'm a grown man, I have a stable job, and I WATCH A SHOW FOR LITTLE GIRLS AND also like to comb my pony's hair..."
That's not to say that all fans of the show aren't pathetic, I mean you can go to this channel right here:
http://www.youtube.com/user/airlessarchives69 (not for the faint of heart, Jesus Christ believe me on this). But typically most people who like the show outside of its intended demographic are just adults who like cartoons. It's just unfortunate that so many of the creepy ones are so vocal about this show.
I still watch cartoons. I fuckin' love cartoons! I watch Regular Show and Adventure Time, always watchin' the new episodes of Bob's Burgers and Archer when they come out, I really don't see me watching those as any different. Ok, well sort of because I don't try and force them in peoples faces like I've seen some bronies do with Friendship is Magic.
But it's not the entire fanbase, just a rather large, really fucking irritating-ass vocal minority.