Analyzing the actions and/or writings of mass murderers in hopes of being able to blame one’s political opponents is not an admirable impulse. The El Paso shooter wrote that his views predate President Trump, but I notice that didn’t stop motivated people from blaming Trump and his “polarizing ideas.”
If we have to play this game, I think I could make an equally good case for “polarizing ideas” on the left. e.g., “When I’m president, I will decriminalize border crossings. People will be coming in from everywhere and when they get here, you’re going to be paying for their healthcare and education, all the way through college. Oh you’re trying to save up a down payment for a house? That’s too bad. Maybe they’ll take your job too. By the way, if you don’t think this is a good idea, you are a deplorable person. You’re a racist. You’re a white supremacist. You’re a Nazi. What do you think about that?” Is that a polarizing idea? I can imagine some unhinged person thinking, “What do I think about it? I’ll show you what I think about it.”