Short answer rap music and a curious mind.
But what's more impressive is how thick of a shell it cracked, my step father who pretty much raised me was/is a klansman and so is his farther, brothers, etc. This was an old fashioned family too my. Mother didn't speak unless spoken to my sisters were expected to marry who my step father chose, this was Normal to us. I was expecting to find a woman to marry and start a family as soon as I was 18. I'm 23 now so this was recent, my step father beat my older sister black and blue for sleeping with a black man. He always told us that black people are rapist and gang bangers, and that Mexican while hard workers are all dirty people and will never amount to anything useful aside from cheap labor. He controlled what we watched and played to reinforce his beliefs in us. On top of this he was a devout Christian ( I was a closeted atheist since 16, but he would have literally killed me of he knew) he believed that gay people should be killed along side of atheist and Muslims (he wasn't focused on Jews for whatever reason)
I had never met a person of color until I was 17 so I never experienced anything first hand to contradict what I was told.
Some time in my late teens I discovered rap and was obsessed, first song I heard was by 2pac and I was obsessed, well as I learned more it lead me to Martin Luther King Jr and what he did for people of color. At some point I broke down crying because I realized everything I was told was a lie. When I realized I was an atheist I decided I couldn't operate under my old mind set so I needed something to replace it and decided to go with the speech that broke my hatred.
I decided I would judge everyone based on their actions not the color of their skin or who they prefer to sleep with.