Sticking to answer the OP's question:
First, let me start making myself clear: I am a fan of the show and therefore, my view is most probably biased.
But I do think that it elicits much more hate than love. I mean, I never, ever saw a collect of money (think about it: people willing to give hard earned money not for a good cause, but rather against it) in order to ban fans of a show or a subset of forum users or a crusade of fake copyright infringement alerts on youtube in order to remove videos. Never in my 28 years of life. Which is kinda perplexing: people get completely riled up for
a goddam cartoon. I mean, people do not mobilize in order to put out of their forums objetively harmful individuals (say, racists, bigots, homophobes, etc), nor started a campaign to, say, remove Glenn Beck videos from Youtube. And this is coming from someone who considers himself a part of anime - gaf, which means that I am used to the whole spiel of "ololol pedo animu lawl", but seriously, I have never seen such an amount of bile for such a silly subject.
People claim that all of this is because of obnoxorious fans, short of like the final fantasy VII hate. I don't deny that there are obnoxorious fans and stupid people among the whole "brony" community, but every single community have them, so why the extra amount of hate (and effort) putted into it? Bronies aren't particulary more smug than say, Apple fans, nor more fanatically loyal than Nintendo fans or more insistent than the whole "Euro soccer VS American soccer" crowd, to give a couple of examples.
The whole meme overdose explanation is a bit tad, well, baffling. I know that overexposition can grate some people (understandably), but it still fall short in order to explain it. I mean, every community have their own memes, and I do enjoy them without needing to be into them, and the same goes for pony memes. I know many people that don't give a fuck about the show, but still love the whole sillyness and parodies behind it, some of them are
downright brilliant.
What I usually found is a sense of contempt and a bajillion people tryint to convice me that I don't
really like the series, as if we are all under a collective spell, fad, irony or deluding ourselves or whatever, and what should I be watching instead, mixed with a heavy dose of sexual insecurity, too. It reminds me way too much of the same attitude that my own ex girlfriend found out during highschool for liking "un-girly" stuff like comic books, videogames, and RPGs. Shuddenly she was surrounded of other girls preaching her about how she was less of a women for daring to abandon the herd, and how she couldn't possibly really like
these things. Now the same is happening to us men, or so it seems, and I think that this is key to understand the disproportional amount of hate that this show and community generates. Social gender roles subversions inside male - centric, brodude nerdish communities seems like a subject primed for hate.
About why the people love it, when viewed from the outside, people seems to belive that every single bronie thinks that My Little Pony is the best cartoon ever created, which is far from true. I personally think that it is a cute, clever, funny little series. And that of course, it lacks the dramatic weight of series like Samurai Jack or Avatar, the great animation of animes like Kemonozume, or the sheer creativity of shows like Kaiba. I love it because it is a show that allows me to relax and forget about the world's cinism, short of like some people defines Aria as a "healing anime", or enjoys Azumanga Daioh. It is a mostly rare feat: comedy is hard to pull off without being obnoxorious, innocence is hard to make without it being diabetes inducing, and is hard to be witty without being a smartass, yet this show manages to do all these things right.
About the whole level of dedication putted into it by the fandom, let me tell you a little bit of my personal background. I am into politics, and I have to deal constantly with ginormous, treacherous douchebags while trying to stay honest and do what is best for my community in the middle of an extremely hostile enviroment. It grates me. And MLP generates the opposite effect on me. Oh, I
do enjoy mature, intellectually challenging books and series. I love my Game of Thrones and Murakami books, but I really can't spend too much time on these worlds once I am back into my dairy life. MLP is just a nice place to be, so to speak. And its aesthethic and simplicity makes it way easier to edit, adapt and deal with, hence the neverending supply of fanart.
There's really not too much else, really. We enjoy it and think that it has a kinda universal appeal, short of like a Pixar film (which yes: are much superior. But you get my idea). And the whole warm, fuzzy feeling of the series is much welcomed in an overtly cynical world, and sometimes it even permeates the community itself, which is great. But it's one of this things that one has to experience for oneself in order to "get it", me thinks. Still, I hope that I have been able to offer a bit of insight into the OP's initial questions.