I will now attempt to explain the My Little Pony: Friendship is Magic phenomenon to those wondering what the hell is wrong with all these guys. First, some myth vs. reality.
Myth: My Little Pony is only for little girls.
Reality: Little girls are it's target demographic, yes. But unlike most media targeted at little girls, this one is not complete tripe (I will qualify this later).
Myth: Bronies are just trolls who only watch the show for the lulz they get from pushing it in everyone's faces.
Reality: Well, actually, this one is mostly true. The lulz potential this show generates is tremendous. But if this were the only reason they watched it, the show's popularity would have started shrinking long ago. The truth is that these people, trolls or not, truly enjoy watching the show and love nothing more than trying to get other people to enjoy it with them.
If someone is trolling you with the show, believe it or not, they are genuinely trying to get you to love it as much as they do. The scary part is that the troll aspect of this attempt means that refusing to watch the show only feeds them. Like any troll, the best defense is to ignore them completely. DO NOT make fun of a Brony. It will only make him stronger and he will immediately commence firing his friendship cannons at you. This is a new breed of troll born, not out of hate, but love and tolerance. Either give up and watch the show, or be destroyed.
Now I will go through a step-by-step explanation of how one becomes a true Brony. The individual paths one takes may vary so this may differ from someone else's experience. But this, I think, is one of the most common.
Step one: An episode is watched. If it is any episode other than the first two, they skip the next step, but in the interest of completeness, let's say they started with the first one.
Step two: "This show is complete crap." This may not have been everyone's reaction, but it is a perfectly reasonable one. The first two episodes offer very little in the way of intelligent storytelling and as much genuinely amusing humor. But, somewhere in his mind, he will acknowledge that the animation is soothing to observe and the excellent voice-acting goes a long way towards making even sub-par dialogue tolerable to hear. Still, the plot is dull and it is obvious to him that this show is definitely catering to young girls and he would rather be crucified than be caught watching it.
Step three: ???????
Step four: The previous step may have involved some form of cosmic ray or lizard-man mind control conspiracy but for whatever reason, he makes it to the third episode. The pilot arc completed, a glimmer of actual substance begins to shine through the muck of rainbows and flowers. However, the truth of the matter is, at this point, he is likely purely in it for the lulz. He still hates the show but thinks the easy trolling it provides is worth the torture. Few make it father than this point purely on the basis of actually enjoying watching it.
Step five: The turning point. The nameless force that propels him from episode to episode brings him to the series' 5th installment. Plot wise, this episode is nothing special. The writing has caught up to the animation and VA quality by this point (opinions on this may vary), but really it's just an episode like any other. However, there is a moment in this episode that, gently but firmly, brings to light something that has been growing invisibly in this almost-brony's mind. Without realizing it, he has become emotionally invested in the characters. Whether he likes it or not, he really cares what happens to them. He still denies the attraction, but he is unable to laugh at their pain or cringe at their joy.
Step six: Bronydom. He makes it to the current episode. How this came to be, he cannot understand, but over the course of watching the show, his reasons for continuing on have shifted. Rather than collecting troll material, he really truly wants to watch the next adventure in friendship. There were even parts that were unequivocally hilarious and moments of awesome too glorious to express to one who has not seen the show. He must have more.
Step seven (optional): The virus. As he eagerly waits for the next episode, he seeks out other bronies to party with Pinkie Pie style. But as fun as they are to converse with, He must convert others to share this joy with. They must see the light. And if they don't? Well, trolling them is still hilarious. It's win-win. The power of friendship he now possesses is intoxicating. Much like a zombie, he must now feed. His victims will either be turned or consumed completely. And he is not alone.
TL;DR- Resistance is fu- nvm, just read all that up there or don't post.
I hope that answers everypony's questions.
EDIT: Some Bronies are offended that I refer to them as a new breed of troll, so I'll reiterate the point I made that they do genuinely enjoy the show. They don't have to be in it for the lulz, but it is an added bonus for those who wish to partake, so I've made step 7 optional.