There aren't many things that I find more vile than racism. Really any of the "-isms" are like nails on a chalkboard to me, whether it's racism, misogyny, homophobia, xenophobia, etc. If you fundamentally don't like a group of people who are in some way different from you, that's just the worst you can be. So when people are standing up and saying, "This has to change," why would you push back against that?
I can't entirely accept that environment plays a part in this. Growing up in the days of integration, to today when my social and professional circles are diverse, I can see why I would find racism so absurd and rage-inducing. Even as the white guy in the room, you're talking about marginalizing the people that I love and respect. It's not a struggle to see why I would stand with the people tired of being marginalized. But even environment isn't the whole story. When, as a child, my grandfather or uncle would make racist jokes, it made me deeply uncomfortable, and I would say as much by the time I was a teenager. Even as a child, I knew right from wrong.
Part of it is certainly that there's a luxury, yeah, a privilege, to being white. You could observe that racism isn't your problem. Race has certainly played no part in my success or failure, ever. It never will. It won't affect my child either. I firmly believe that this is where a sense of morality and obligation to community comes in. "Those people" are your community... why would you not advocate on their behalf? I don't think it's a hard leap to walk in the shoes of someone concerned that they're two and a half times more likely to die at the hands of law enforcement for the color of their skin. It's a thing when your house is worth 40% more if it doesn't appear too "black." These aren't imaginary things. I feel that some people aren't even willing to acknowledge that racism exsits.
There is no more important thing. We can differ and "agree to disagree" as people like to say when they cop out of engaging in the discussion, when it comes to things like fiscal and foreign policy, or who pays for healthcare. But not this. There may be two sides to the issue, but only one is morally correct. Furthermore, if you truly love America and its values, you have to believe that racism is at its core anti-American. I would make a similar argument about any claim to Christianity, but I'm not one to define faith for you. The most fundamental Christian values include compassion and peace toward your fellow humans.
Being against racism is not a left or right issue, but it is the issue, and America's greatest failure. We can't let it persist for another 300 years.