I went to Urban Dictionary.com to seek understanding on the matter, but it was hard to come up with general consensus, as there are 108 definitions. The definition with the highest votes states:
A person that simply cannot be happy for another person's success. So rather than be happy they make a point of exposing a flaw in that person. Hating, the result of being a hater, is not exactly jealousy. The hater doesnt really want to be the person he or she hates, rather the hater wants to knock somelse down a notch.
My argument is for the second most popular definition:
Overused word that people like to use just because someone else expresses a dislike for a certain individual.
Criticism can be harsh, and sometimes singed with hate. However, the need to not be criticized is a founding principle of bitchassness. Anyone can bang on a piano and writhe their head, singing what comes to mind, but there's only one Stevie Wonder. Public opinion gauges your greatness. It's a hard fact of life. Some achieve it after their lifetime, but they were great just the same. How can you be considered great with no display of the true measure of your skills. Ascending to the next level requires new challenges. The monetary system will always be a rat race, but champions thrive for conquest in contest.
That being said: You cease to be a hater when your observations are proven to be truth.