Why do we hate? Presumably all emotions serve a purpose. What is the purpose of hate?
It is clear why some emotions exist. Fear, for example, serves to keep us safe from things we deem harmful. Anger, within reason, is a reaction to something we find objectionable and that helps us to learn to interact with others and also to protect ourselves.
Hate and love are opposite ends of the same scale, so the question could also be "Why do we love?" That seems to be easier to answer, however. It appears that love is the ultimate objective - the highest level of human development.
So then why do we hate? What purpose does it serve? Is it because of our own insecurities? Do we need to feel superior? Is the ego the hatemonger in us?
Could it be that our propensity to hate (or conversely, love) is a measure of our spiritual development?