I don't care if it rubs people the wrong way, because my motivations are pure and it is applicable.
We don't know if he actually has a mental health issue, but you know one of the first things the police are going to do when they arrest him? Run a mental health evaluation. Why? Because statistics show that people who commit crimes like this are waaaaay more likely to have a mental disability.
So if we want to prevent a huge number of these crazy racist nutbars from actually committing these crimes, we need to fight the root causes. Which go beyond merely fixing the institutional racism and whatnot, but also addressing the mental health issues in this country. Mental Health Care is wildly underfunded in this country.
I am not "assuming" he has a mental disability, but I do think the odds are good - because the statistics say so. It doesn't mean I'm excusing his behavior or that I think he's not a racist asshole who took the lives of many innocent people callously. The whole situation breaks my heart, because it shows how far we have to come in so many different areas.
In other words, we can acknowledge multiple possible complexities of a situation like this without making any excuse for the behavior and while being proactive to prevent future cases.
It doesn't necessarily simplify the issue, but by the very nature of the way people utilize it - very much in a good vs. evil storybook painting way - it often muddies the reality, painting over it with broad strokes and awkward lines, so that in the end we're left with caricatures of human beings instead of incredibly complex organisms who can fail in any number of zillion ways. Evil is just a black/white indicator. Yes, this dude is a bad guy. Where does that leave us?