The bullying I went through as a teen damaged me in ways beyond my own comprehension. When I was going through those times, I got by while repeating the motto: "Relationships are about winners and losers. When they dissolve, there's always a winner and loser. Don't be the loser."
I knew what they were doing was wrong and that God would hand out judgment at the appropriate time, but years after all that torment ended I'm beginning to realize that any justice that's served is done so by ourselves.
Bullies will never realize the extent of their actions until they find the source of them. Your right...it's hard to hate someone who, if you were in their shoes, you'd probably be no different. Then you may direct your anger towards the people and circumstances that made that person who he/she is, but you'll never find the true cause.
The trick, after all the abuse is over, is to realize that we're all people who at some time have been hurt and that showing compassion for one another is the only way to heal.