Anime has hate on several levels.
Anime, in its basic form, is cheap animation. Lack of in-between drawings, repeated/cycling backgrounds and fast production cycles make anime a cheap medium. The (US) animation community knows this and while some embrace it for its storytelling, a lot of die hard animators HATE anime because it's cheaply made and drawn.
Some hate anime because it's saturated the market. The more you see something, the more it can get sick. In the early 80s, anime was a rarity, not now.
Others hate it because it's recycled stories and characters. To the Japanese, the beauty is the journey...in the US, it's all about the ending of the story. Some hate anime because a lot of them just END horribly or have no resolve.
That's just several reasons...though I think BIG reasons. There are more, but I only have so much space to type.