I would infer that even in Japan, Sakura is RELATIVELY disliked. My inference is based on the Japanese popularity polls released with manga chapters (with the assumption that these polls are a good statistical sample of the fandom population so that statistical inference is valid) found here
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Notice that Sakuras zenith in popularity is right at the beginning where only the main characters (Naruto, Sasuke and Kakashi aside from her) have the spotlight and supporting characters are just introduced (consider also the fact that Sakura in the beginning is introduced as a superficial Sasuke fangirl). Now as the manga progressed, notice the trend that
1. Sakuras popularity declined, never again to reach top 5 status
2. The other main characters (Naruto, Sasuke and Kakashi) popularity only fluctuated in the top 5 position but did not decline
3. Characters who got very little panel time in comparison to Sakura started to overtake her
The inescapable conclusion from this is that Sakura, unlike the other main characters, failed to garner positive reception from the general fanbase. Hinata (the only female character to surpass Sakura on several polls) in my opinion is a one dimensional fodder character, that she surpassed Sakura on popularity on several occasions does imply a lack of positive reception of Sakura in the fan population in Japan.
Your claim that western fans sent death threats is ridiculous to put it VERY mildly, care to even attempt to corroborate it?