I think hate is a strong word, and I think that it involves the same kind of emotions. You have to care for that person to let them take control of your emotions to let you feel that way. Often when people are consumed with their hate for a person, it is just reflecting the hurt they are feeling inside, otherwise they wouldn't think about it so much.
I think someone can hate someone they once loved, and actually I think it is the ones we loved before that we can say we HATE! Otherwise, I think they just may annoy us, or bother us. But it's those that have disappointed us, or showed us a side we didn't know and therefore we take it to the complete opposite of emotions to help us reason why they did the things they did, and help us cope. Not in a healthy way, I might add.