I used to think that this recent flood of hatred from Sakura was due to the fact that Sakura is getting screentime and powerups instead of characters that some fans would prefer. I mean, I've always thought that people had a very skewed view of what Sakura was really all about, and that she got a lot, and I mean A LOT, of unnecessary hate over the years. But now, I think a lot of this is just personal bias against her. I mean, think about it, what were the main reasons people hated her?
1) Being useless. This one has no merit anymore. She has taken over Tsunade's "top medical ninja" position, which was very important when Tsunade did it, yet it is suddenly "less" important when Sakura does it. She has developed the seal on her forehead, which provides her with more than her regular strength, which is already quite frightening in itself. She gave a speech on helping Naruto, and again, when it is done by Hinata it is the most useful thing in the world, even promoting Hinata's status up to "Maine Heroine", yet when Sakura does something similar it becomes "completely unnecessary and useless". She has also assisted in healing Naruto, Kakashi, and many other Shinobi, and this is all just in her recent developments in this war arc, mind you. So, clearly, she is not useless anymore, so that should not be a reason people hate her, right?
2)Sakura's irrational feelings for Sasuke. With this one, I can actually see the dislike. Granted, I have never disliked her for this, but I can see where it is coming from. It is not the reason for hating her for this, per say, that it ridiculous, but rather the double standards involved. People seem to "hate" her for holding onto these feelings for Sasuke, when he has absolutely no interest in her whatsoever, and he tried to kill her on multiple occasions. And I admit, it does hold her character back a bit. However, people cant stand that she might be getting over him, either, if you see what I mean. Sakura getting over Sasuke can be linked to her acting on her feelings for Naruto, which also exist. What I'm trying to say, I guess, is that people hate her for her feelings for Sasuke, but also hate it when there is evidence that she is moving on from Sasuke. It's a horrible double standard, in my opinion.
3)Sakura's development of romantic feelings for Naruto. This one is directly linked with Number 2, and I think its a killer. In my opinion, nothing but good would come out of Sakura falling for Naruto, which I believe she is doing/already has done. Sakura would be happy, and so would Naruto. And since she would have already been in love with him, he would not be a second choice. Well, for some fans, it seems that seeing both Naruto and Sakura happy is just unbearable. I mean, the slightest indication of romantic intentions from either side is constantly rebutted against, normally with remarks that hold no water. This is just another example that people will hate her no matter what she does.
4)Sakura treats Naruto terribly. Oh for sure, had to include this one. She heals him, cries for him, tries to protect him, defends him against Sasuke, tells the alliance to help him, runs to him in his K4 mode and gets injured, worries about him, hugs him, smiles at him, believes in him, defends his goals, fights to defend him in the Shinobi War, thinks of his feelings, and tries to comfort him when Jiraiya dies. But yeah, she's a horrible person all the way.
5)Not as strong as Naruto and Sasuke. This is really the only other reason that I can think of that's worth mentioning, and I can't help but think, really? No one, in the entire manga at this time, is as much of a powerhouse as Naruto and Sasuke. And these people expect Sakura to be on par with them? No offense, I love Sakura, but that is not possible, for anyone, except maybe the Edo-Hokages and Madara, maybe. Sakura is now one of the strongest in the K11, but she's not OP like her teammates. This is so unjustified...ugh.
Well now that these reasons are listed, it seems as though all of them are either double standards or innacurate. There are other reasons why she's hated, but I didn't feel like listing them, because they're kinda....pointless. This is why I think that most of her hate nowadays stems form more personal bias against her character. People can't seem to find really legitimate reasons to dislike her character anymore, other than the pairing-related petty stuff, so they look to bashing her. This is just what I've seen lately, I'm not saying any of this is fact, heck for all I know, it could all be wrong. 
Oh geez, I'm sorry this has gotten so long, I kind of ranted. Heh, I'm still a newbie, so what do you expect?