Do you have an opinion (whether positive or negative) about the MLP:FIM fandom?
My opinion is more dependant on the people rather than the fandom itself. I have nothing wrong with the fandom as it's like any other fandom; it can be good, but it can also be pure cancer. Regarfless I've met some really awesome people who like MLP:FIM; one even being my best friend, but I have also met a lot of people who like it, but are regardless quite unsettling to be around for instance, I once had a "neckbeard" wearing a MLP hat come up to me and try to hit on me when I was with my boyfriend just because I had a Pokemon shirt on.
Then again, what I'm trying to explain is that it's not the fandom, but rather some individuals who are apart of said fandom that can create a negative experience and view of it.
Do you think there are any legitimate reasons to dislike said fandom?
I think as I said, the likeness of some individuals within the fandom is what is causing a dislike towards it. I've heard stories where at one of the movie premiers, a father with his daughter who is a huge fan of the series were attacked by the generalisation of a bunch of overweight middle age men and were called "filthy casuals" as a result, but then again, as I also said, any fandom is like that.
I personally think the anime fandom is probably worse than the MLP one, but it's dependant on who is asked.
Do you think that brony haters are misinformed/misguided/ect?
Immensely. Any fandom has it's flaws whether it be the HP, anime/manga, MLP or furry fandoms, but it doesn't represent the fandom as a whole. I have met people who are pardon my French, f**king disgusting from the anime fandom in which I am apart of yet I have met people who are super cool like my best friend who is a brony. I think at the end of the day, we just should respect each others fandoms as long as we aren't hurting anyone else. There is no perfect fandom. Some are worse than others, yes, but we just need to find a middle ground and that is we're also dorks at the end of the day.
But seriously though, I probably will never join it as I'm not a fan of the show. Personal preference bro.