Its no secret that Sakura is probably the most disliked character in the Naruto fan population. The most common reason Ive generally seen is that shes "useless" but I dont think thats true, her overall feats throughout the manga far outweigh any other character in the K11 bar Naruto.
I think the reason she is hated is simply her personality/character: shes whiny, temperamental, loud, impulsive and sentimental, i.e., she is the embodiment of the word b!tch (its like shes on her period 24/7 and this is especially true of the animes portrayal of her character).
When I watched anime, I developed an instinctive dislike of her character for these reasons, I see complaints about her role in the manga as rationalization tbh, I think those of us who dislike her simply dislike her essential character traits.
thats also why i dislike her ....and there are some other reasons too
-her unhealthy obsession towards sasuke
-her treatment of naruto (sumtime naruto deserves it but other time she is simply acting like a b**ch)
-she lied to naruto (whatever reasons she had ....she shouldn't have lied that she loved naruto)
and you know her whole characterization from part1
this is what i understand from sakura's character ....
(try to imagine annoying inner sakura's voice saying this)
"hey i'm sakura, i'm the typical heroine-weak girl in a manga who goes after bad boy sasuke..i know the nice guy naruto likes me but i'll push away naruto, tell him i hate him and say he is annoying because of his immature crush towards me ... by the way i have the same kind of immature crush towards sasuke .....then my crush sasuke goes rouge i cant stop him and i'm weak to bring him back by myself.....oh wait the nice guy naruto is good in talk-no-jutsu and strong too so i'll ask him to do the dangerous mission of bringing back as my crush sasuke.......also in the mean time i'll go along with naruto for missions and play with his feelings ,hint a more than friends relationship so that if sasuke doesn't ever return i'll have the nice guy naruto to protect me ,do my bidding etc.... but if sasuke returns i'll totally ditch naruto and hump onto sasuke's d**k"
to tell you the truth i didn't dislike her this much in the beginning......but after hearing the sakura fanboys in NB make her sound like "the savior of the narutoverse" it just got worse