Disclaimer: I do not own Naruto nor the quotes.
Hatred
"Happy families are all alike; every unhappy family is unhappy in its own way."
-Leo Tolstoy (1828 – 1910), Anna Karenina, Chapter 1, first line
Sakura hates weasels. They are her least favorite animal. Misfortune clings to them like plague follows the rat. It is an all-consuming hatred that burns far hotter than the sun that shines down on her village.
Haruno Sakura hates weasels far more than anyone will ever know; perhaps far more than Sasuke. She loathes weasels because a weasel took away everything. A weasel took away her boys.
A weasel took away Kakashi from his one remaining student so Sakura had to find someone else to be her mentor.
A weasel led Sasuke away from the village and his chance at finding happiness with his team; all for an empty power.
A weasel took away Naruto by forcing him to make a stupid promise that could have gotten him killed.
A weasel took away Sasuke's family.
A weasel took away Sai's chance at a normal life.
A weasel stole Sakura's happiness.
So Sakura hates weasels and she hates Itachi far more than she hates weasels; perhaps because he is named for one.
Sasuke told Naruto everything, and it was only later that Sakura was told what had happened. She believes that for all his repute as a child prodigy and a genius, Itachi was a fool. He had refused to be selfish for once in his life, and would not, could not, consider the third option.
So Sakura hates Itachi because when she thinks about that third option, she can't help but imagine what could have been. Sasuke would never have left those he loved for the power to chase a vengeance that would quickly turn to ash. Naruto would never have had to make that stupid promise. And her happiness would be intact.
Sakura hates weasels.
"We hate some persons because we do not know them; and we will not know them because we hate them."
-Charles Caleb Colton (1780 – 1832)