(CNN) The first thing I saw on my Facebook feed after news of the shooting at Tree of Life synagogue broke was a photo my friend posted from his daughter's bat mitzvah. In it, he and his wife proudly looked on as their daughter read from the Torah -- documenting her journey from childhood to adulthood.

As a former leader of a white supremacist group in the late 1980s and early 1990s, seeing images of Jewish, black, Latino, Asian and Muslim children today make me ask myself how I could have been so deranged as to think that they were anything less than children.

The answer is: fear.

Fear has the capacity to destroy us. Everything I did back then was rooted in fear, as was every genocide in human history. And nationalism cannot exist without fear: fear of losing, fear of others, fear of change.

Thus, it's no surprise that nationalism and genocide often go hand in hand. As George Orwell wrote in his essay on nationalism , the spiritual sickness of it is by no means restricted to nations and geographic borders.

Throughout human history -- from our earliest tribal skirmishes through the Spanish Inquisition, the Holocaust, Stalin's purges, the 16th Street Baptist Church bombing, the Rwandan genocide, the mass murders at the Oak Creek gurdwara and Emanuel AME and up to the most recent tragedy at the Tree of Life synagogue in Pittsburgh -- nationalist thinking has led to unspeakable suffering.

Before the brutal mass murder of 11 Jews on Saturday morning, the shooter posted , "HIAS likes to bring invaders in that kill our people. I can't sit by and watch my people get slaughtered. Screw your optics, I'm going in." HIAS is a Jewish nonprofit that helps immigrants and refugees resettle in the United States, in the same way a Christian agency helped my friend Heval Kelli and his family settle in the United States as refugees from Syria.

Note the intense fear in the shooter's statement. He had himself convinced that his people were being slaughtered.

Looking back at how my twisted mind operated when I was a white nationalist, I spun every shred of information to suit that same narrative of fear. They are coming for us. And nationalism was the context necessary to focus fear into an us/them binary.

I was incredibly fortunate that the exhaustion of constant spin and fear, along with the loving guidance of my parents and brave people who refused to capitulate to my hostility, eventually led me from nationalism to where I am today: a place in which I embrace diversity, and the constant change that creates it.

Embracing those truths is critical to reforming nationalist thinking. It is how we unlearn fear and separatism and find not only peace with change, but joy as well. That is how we create a society where all are valued and included.

The miserable, suffering man who took 11 lives at Tree of Life synagogue in a despicable act of cowardice was driven by the same intention as his peers who have engaged in equally horrifying acts of violence. The shooters behind the attacks on the Sikh Temple of Wisconsin and Emanuel AME, and the bombers behind the Boston Marathon attack, all shared one objective: to break our faith in humanity with fear.

We cannot truly defy them and their intention without understanding this dynamic. We are all human beings. And we are all in this together. We must look upon our brothers and sisters stricken with maladies like nationalism as loved ones who need help, rather than monsters who cannot be spoken to.

At one time, they were innocent children, as beautiful and full of potential as any other. Something went horribly wrong between then and now. As challenging as they can be, compassion and forgiveness are essential weapons in the fight for a society where all children are treasured as they should be.

This doesn't mean that force is off the table when it comes to stopping sick people from doing harm. It does mean that if said force isn't soundly rooted in compassion, it can only result in more of the fear and separatism that nationalism requires to function.

The most devastating blow that can be dealt to ideologies like nationalism is to demonstrate that the fear they are rooted in is utterly unfounded. And, as we ask people whose suffering led them to such toxic ideas to be brave and open to the possibility that their fears are unnecessary, we have to walk the walk by not being afraid of them.

Diversity is one of my greatest loves in life. In the 2½ decades since I left hate groups, I've changed fearful, unhealthy habits into vigorous, uplifting practices. I'm mindful each day that my perception is a lens that focuses reality in the same way my eyeglasses focus vision. I can shape this lens any way that I choose.

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As human beings, we find what we look for in life. While it is much more difficult to exercise the will required to look for reasons to love, to have faith, to serve and to wonder than it is to give up and let fear make our decisions, I choose to put in the work to do so.

Knowing what the alternatives look like, bearing witness to the suffering caused when fear and ignorance are unchallenged, leaves no other choice.

I write this from my heart, broken yet again -- this time with deep love and sadness for the Jewish community of Squirrel Hill, the Jewish community worldwide and all of humanity.

We are one.