Eveyrone has their own opinion. I have never had a problem, with someone not liking Fairy Tail, but reasons of 99% of them who don't like Fairy Tail are shit, more or less. I like Fairy Tail, it's plot isn't so great, it's full of fan service, hyped characters always lose, and out of mangas I read (Naruto, Bleach, OP, DB, Shaman King) it's worst, still it's chapters are enjoyable with some great humor. Even while I agree that it's not greatest manga, it's pretty much one of my favorite.
I remember having huge debate about critism. I rememeber arguments "Like you are not a fan, since you always shit on it", when I further explained things to tham smarters members got it (you can't explain to plonkler that he is wrong) and they argument was "Oh, I see, when I read chapter I always concentrate on good things (my fav. character, action, humor, Lucy's ass, etc) " which make them enjoy chapter more. I tried that method and really it's great. When you are concentration on good things, it's easier to forgot about bad things in chapter (no story progression, bad humor, bad characterization, Lucy's ass again). I am mainly saying this about other mangas, because when it comes to Fairy Tail, it seems people don't concentrate on good things, which help them forgot about bad things, but they actually concetrate on bad things, which make them forget about good things.
Now to return on their arguments:
It's annoying - I don't know where this is coming from, I can constructive critic Fairy Tail, a lot, but there is no much parts where I can say it's boring.
Nakama power - As part of the shonen, it's logical, this is not valid argument. Point of Shonen mangas is good beats bad, that with your friends you can do everything, you see that motif in Bleach, Naruto, One Piece. They say Natsu always beat bad guy, after his ass being kicked, well I am not so sure how Luffy was able to beat Crocodile (not to mention that this happen in One Piece, probably greates manga ever).
Fanservice - really bad part of the manga. But people who say this, don't really understand what fan service really is. You will see members complain about nudity, but same members will never complain, about Itachi's huge role in War (Naruto) or Byakuya's miraculous survival (Bleach), yes that's also type of fan service and it was just on top of my head.
Rip off - I will not even bother with this one.
That was just on top of my head.
I really not have a problem with someone not liking Fairy Tail, I have problem with their non constructive critism aka hate.