Imagine growing up hearing from those you love and trust that certain groups of people are evil. In fact, these people are so bad, so wrong, that God himself will punish them. Imagine absorbing this hatred deep into your bones. Imagine that you then discover, at some point in your adolescence, that you are one of these people.

They are the hated. You are the hated.

We don’t know the details of Omar Mateen’s sexuality. Perhaps he did not fully understand.

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But according to some, Mateen expressed romantic interest in men. A classmate from his 2006 police academy class told the Palm Beach Post that Mateen had asked him out. Sometimes, after class, Mateen would go with friends to gay nightclubs, the classmate said.

And we know that in a video made after the shooting, Mateen’s father said, "God himself will give punishment to homosexuality." It’s conceivable that this is a sentiment Mateen heard more than once.

We will never understand what triggered Mateen. But there is abundant evidence that the prejudice we face is toxic. And when anti-gay prejudice comes from parents or religion, the effect is profound. According to University of Tennessee Knoxville psychology professor Dawn Szymanski, research shows that parental rejection of one’s sexual identity is linked to traumatic internalized negativity - what psychologists call "internalized homonegativity" or "internalized stigma." The same is true when a person belongs to a religion that rejects homosexuality.

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One consequence of this internalized stigma is violence: Studies of same-sex couples show that internalized homophobia is significant predictor of violence within a relationship. Self-hatred also creates profound psychological distress: One meta-analysis found that higher levels of internalized anti-gay stigma were correlated with worse mental health. The psychological distress can include anxiety, depression, poor self-esteem and hyperarousal - a state of increased tension that includes irritability, anger and aggression.

The stress caused by internal stigma can evoke a biological response. According to Stephanie Budge, a psychology professor at the University of Wisconsin at Madison, there is broad consensus in the research community that "minority stress" - including internalized self-hatred - creates massive physical health problems. According to the Mayo Clinic, this kind of cumulative stress disrupts almost all the body’s processes. Indeed, gay people who live in communities with high levels of anti-gay prejudice have a life expectancy that is shorter by 12 years.

Anti-gay prejudice is especially pernicious because it creeps into the intimacy of one’s own family. For other forms of bias - racism, for example, or prejudice based on one’s religion - the family can be a refuge against the hatred of the outside world. But anti-gay prejudice is different. The hatred comes from not outsiders, but from loved ones. Parents’ rejection of their children is the one of the biggest reasons as many as 40 percent of homeless youths are LGBT.

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Will Cox, a research scientist at the University of Wisconsin-Madison who studies prejudice, was one of these kids. He grew up in a strict Mormon household and was rejected by his parents when he came out as gay.

"I felt guilty," he says. "I’d pray for forgiveness. The religious piece was so strong — at one point I had email exchanges with my parents discussing same-sex marriage and my mom said: ’Will seems to be making a lot of good points. Do you think that is because Lucifer is influencing our thoughts?’ "

Politicians will continue to use "radical Islam" as a culprit. But it’s not clear that Mateen was motivated by ideology; indeed, he claimed to support a jumble of groups with conflicting points of view. On the other hand, his ex-wife told CNN, "It doesn’t surprise me that he was leading two totally different lives and was in such deep conflict within himself." No psychologist, says Budge, would say this conflict was the triggering cause. But it’s impossible to imagine that the deep distress of this internal struggle did not contribute in some way to Mateen’s mental state.
Hours after the Orlando massacre, Sacramento pastor Roger Jimenez delivered a hate-filled speech in which he expressed happiness that the tragedy had happened. He said: "The Bible says they’re wicked, they’re vile, they’re predators. And they deserve the death penalty for what they do."

Imagine a young person sitting in his congregation, listening. Imagine this young person absorbing that certain people deserve to die because of who they are. Now imagine that child growing up to discover that he is gay. He, too, deserves to die. Imagine the chaos and self-hatred growing inside his heart.

Jessica Nordell is a journalist and business consultant.