Hate is only an emotion. The truth is that if you let strong emotions (either good or bad) rule your heart you'll loose the grip on balance placing your own will above anything else and obviously becoming selfish. That's why Jedi are taught to avoid not only bad feelings like hate or greed but also love.
But is this good ? Those who are taught to avoid emotions rather than confront them may become unpredictable once they're put under pressure because emotions rule the life of sentient beings and sooner or later they will surface nevertheless. That's the greates flawl of the Jedi doctrine.
Jedi teachings limit the individual freedom; dark side -on the contrary- encourages a life with little rules or bonds. This may be indeed a sort subtle, inconscious revenge against the Jedi doctrine which is perceived (and, indeed, it may be) flawled, not to mention that a high confidence in the power of the Force sometimes may reinforce the wrong belief of being above the others.
Dark Siders become arrogant, egocentric and the unsatisfaction repressed in years of jedi training may indeed culminate in act of violence (not necessarily physical) to give vent to inner frustrations: that's why Dark Siders seems to hate evertything they couldn't achieve: serenty, love or maybe even a normal life.
In the end, the Dark Side IS selfishness, coming in many subtle ways, for different reasons.
Lucas envisioned the Jedi as a sort of monastic order, following a strict rule of conduct and possessing a deep and incredible knolwedge. The struggle between the light and the dark side is not necessary the struggle between Good and Evil, but between order and chaos. Who said Jedi are good? They might persue the greater good of the galaxy but sometimes they display a form of righteous arrogance and their strict discipline limits their vision of reality luring them into making terrible mistakes. On the other side there is chaos and at its root there is selfishness: the Force is a powerful tool that lure its users into believing to be above the rest of the sentient beings, beyond good and evil. But, in the end, they fail to reach a greater state of enlightment (There' is an interesting analogy with "ubermesch" envisioned by Nietzsche) and they only succeed in playing their own downfall.