for me Sakura represented the growth a normal person from only looking at things superficially, like chasing after a boy because of his looks, clan name and talent alone, and becoming a Ninja (a job) because it sounded cool and follow your friends, even thinking how cool it would be to if you had no rules growing up and can do whatever you want.
Then to grow up, realising there is more to person than just their outside appearance, and judge a person for who they are and not what they are, realising that being a Ninja is not a joke, and you not taking it seriously, puts others at a disadvantage, and they have to work harder to to bring up the slack, and finally realise the importance of family, and not to take them for granted. These are the things most of us learnt when we entered adulthood and Sakura was the representation of that growth.
I don't think a lot of the readers (that hated her) ever understood that, for them, they just saw the first few scenes (made worst in the anime) and judged her for the rest of the series, and I think to a certain extent Kishi (or his editor) encouraged this behaviour from her, like her confession, but not showing the resolution, her unlocking her potential and then requiring to be saved straight away, etc,because as sad as it is, even negativity can work in your favour for a medium as it drives discussion amongst fans, and keeps the series relevant for longer.
I could be wrong here, the trouble wasn't Sakura's characters negativity, but the Hinata hardcore fanbase, they had her on a pedestal and any negativity on her character would be ignored and not be tolerated, they refuse to acknowledge that her knowing that Naruto was being mistreated as a kid, and all he wanted was a friend, yet never doing anything about it, is a big stain on her character, that her obsession with Naruto was not healthy, her actions put not only her but her teammates at risks, and showed that even if she says she acknowledges Naruto she doesn't have the same level of faith in his strength that Sakura does,. Hinata's first action would be to stand in front of him to protect him, Sakura on the other hand believed in him or would stand beside him, or behind him ready to offer support. I think they were more afraid of the Hinata fanbase than the Sakura fanbase backlash.