By simplest definition, a "brony" is a male fan of the "little girl's" animated cartoon show My Little Pony: Friendship is Magic. Hasbro decided to reboot the 1980s franchise "My Little Pony" and did so with a brighter, simpler animation style with larger eyes, more simplified hooves, and a "modern" animation feel. To their immense surprise (and many others') they found a curious demographic of men who latched on to the show.
When a whole host of men whose average age is 21 but yet by definition has an age range of about 15 to 51 start obsessing about a show designed for little girls, it's pretty certain that there will be public attention. Males and females alike tend to police gender roles around men pretty fiercely, and project a lot of concerns about men and how they should behave. And worse, when you consider that in order to buy such things a man has to go into a "girl's" toy aisle - although there have been no overtly reported cases of hostility towards bronies in this context, a 45 year old unmarried man in a fedora casually shopping for pink and bright pastel colors would most certainly make some women think twice about leaving their daughters in that aisle. Even though that's crazy, because there are any of a number of perfectly reasonable explanations as to why a man would be in that aisle - shopping for a daughter or a niece, or, heck - what exactly IS wrong with a man liking a show for little girls?
The whole phenomenon has gone beyond public attention, with two documentary films and mentions on The Howard Stern Show and Stephen Colbert - to outright study. Psychologists in Spartanberg, South Carolina took an interest in who and why some men would openly swan dive into becoming identifiable gender outlaws. It turns out that bronies are no more or less homosexual than anyone else, so the theory that "it's a bunch of gays" doesn't answer the question. What they did notice in further testing is that bronies tended to lower scores in neurotic thinking and behaviour - in other words, relative absence of anger, anxiety, envy or guilt. Whether that was correlational or causal isn't known, but science is starting to clear up what bronies self report: no, they're not gay, they just happen to really like positivity.
What complicates the picture is their self-reporting that they actually happen to enjoy the show for what it is, as well as what it may represent. People wrote off children's cartoons in the 1980s when they went from an art form of the Warner Brothers and Disney eras to being very, very transparent half hour advertising for toys. Plots resolved in 22 minutes, usually by deus ex machina, the same stock animations were used over and over again, and it's a rather rigid and depressing binary. Characters X, Y, and Z never win because they're the bad guys and characters A, B, and C always win because they're the good guys. My Little Pony: Friendship is Magic, from what I gather, happens to be well written, well acted, and contain more engaging and complex stories. Okay, so they're still written to a level that the average eight year old can understand, but the stories usually revolve around some kind of character development - they win not by being muscled brutes who hammer other people or worse, fart rainbows at other people and turn them into born again happy people just because - but by learning something about themselves and using some aspect of their innate personalities. Friendship is important because nobody is an island - what one pony isn't good at, another one is.
I don't remember He-Man or his alter-ego Prince Adam having any goals in life apart from lounging around Eternia waiting for something bad to happen, whereas one of the ponies really wants to get into a flying team. One's a bookworm who loves to read. They take it beyond the Smurf idea of "this one reads, this one lifts weights" to having them pursuing their own personal life goals as well as the goals in the episode. It's also brought up that what makes each pony special in her own way (one is highly generous) is always a two-sided sword (can be generous to a fault).
This I can completely see as engaging television (I've been told that if you watch the show, by about the fourth episode you're likely going to at least appreciate it) and understand why some men would go for it so much. I'd generally feel kind of cheated if the shows of my youth were phoned in and generally about people shooting at each other with "stormtrooper academy" precision for 22 minutes a time.
According to some researchers, there's always some movement that comes around ten years after a notable crisis. The roaring 20s were a reaction to WWI. Beatniks rebelled against WWII. The combined stresses of the Korea and Vietnam wars gave us hippies. The theory is, in addition to men being fatigued at being fed a diet of anger and bullets and big muscles are not only individually deciding to pay attention to something nice, but generationally are basically reacting to the horror and militarization of 9/11.
The other aspect is this: feminism, despite the strawman attacks against it and chracterizations by Rush Limbaugh as "feminazis" and so forth - has made inroads. The first part was getting women to be considered the same as men: they can generally wear pants without being sent to an insane asylum and forced to wear makeup, they can vote, and they've made tremendous inroads into business and trades. But the last mile has always been the "pink and blue" phenomenon - that once you put a pink cap on a baby versus a blue cap, how it's treated and how it's judged change completely. Sure the likes of a Kat Von D can sling tattoos and curse like a stevedore just like the boys, but it's always been highly questionable for men to identify with things that are female.
So the fact that you're having entire groups of men not only rallying explicitly around "a show for little girls" but truly appreciating the "feminine" messages therein - that's a big win for the kind of gender equality that will eventually come with a complete smashing of gender roles. And it seems that public opinion has gone from "ha! fags!" to "well, it's a thing, I guess" to "what exactly IS wrong with liking a well written show promoting friendship and tolerance?"
This is not to say that the show's popularity with men hasn't come with a darker side.
It's one thing for a girl to write "freaky friend fiction" about a series, and another for someone to draw a stylized vulva on a cartoon horse. Naturally Rule 34 applies to everything so there is a subgenre called "clop" which is - and I shudder to actually type this - erotic My Little Pony. Dare I say, "My Little Pony: Friendship With Benefits Is More Magic?". From depictions of the characters interacting sexually to, and God forgive me for having seen this in my research - actual modified MLP plush dolls with masturbatory sleeves made to be "sex dolls". It's not that creepy to do when the characters are adult - but when one of the show's ideas is that a pony achieves ponyhood when she "gets her cutie mark" (euphemism for first menstrual period), a sigil that appears on her flank - we're talking about pre-teens here. Most of the ponies are clearly "adult", with independent lives and so forth, but some aren't, and there's a lot of story ideas relating to coming of age. There's therefore something that creeps me out in this, but here's the thing, it's making me examine my own gender biases. Because when some middle aged women wrote Harry Potter erotic fan fiction, they were writing erotic fiction about children. And some of the scenarios were downright creepy - pairings of Hermione Grainger and Severus Snape are, after all, teacher and student. In theory, I should find them equally abhorrent, but the idea of sexualizing something for little girls still triggers the idea of "grooming" girls which leads me down a very, very dark trail of very internalized gender biases.
And of course, there's also the headache Hasbro has had with the success of the show. There is a LOT of fan-made material, from remixes of the songs used in the show, to deviantart drawings, to outright etsy creations. The generation coming up tends not to understand how copyright works. "Oh, just download it" is a thing. The notion that a property is actually called that for a reason - it's the creative property of HASBRO, is lost on many of them. So whereas Hasbro has been pretty lenient with fan pages and suchlike, it's brought the banhammer down on overzealous use or even people making their own merchandise for sale. "But it's not theirs, it's ours too" opines a young man in "A Brony Tale", unclear that Hasbro actually has to enforce its copyright to keep it. This is not a new problem - Harley Davidson had a problem with people using their logo to make their own merchandise for sale back in the day, which is why some of their fan-made stuff these days simply has a bar and shield that resembles their logo, but isn't. But whereas Harley had to deal with people turning out T-shirts at bike week events, Hasbro is having to make snap decisions about dozens of people monetizing their property - what's something worth keeping because it stimulates demand for their product, and what has to go because it crosses a line or dilutes the brand? Another challenge for the 21st century, especially as how 3d printers are now available on Amazon.
As a Christian, I kind of like watching groups of men hug each other and profess friendship, happiness, and loving other people for who they are. Whatever dark corners exist in the fandom are more than eclipsed by watching people who are clearly outcast in their normal life find a group that appreciates them for who they are. From a combat vet who decided to draw again and found the show as therapy to deal with the horrors of Afghanistan or the young Atlanta DJ getting his college money up by playing MLP-based DJ sets, it seems that "Keep Calm and Brony On" is for the most part a very good thing. If you want to stick a brightly colored button on your fedora and smile at the world around you, more power to you.