I don't know why Betts's (I'm just going to use his last name since it is public knowledge and is easier to type out than the Dayton Shooter) ideology matters in the context of his shooting. If you read the news reports about him you'd be quick to learn about the fact that he was apparently a rampant misogynist and gun freak during his high school days (and obviously after then) he would talk about a list of girls he wanted to rape at his high school, and another list for people who he wanted to kill and apparently was not punished for openly talking about this harshly enough/wasn't talked to about how this was fucked up to have or even joke about. Nothing about being a leftist really speaks volumes about wanting to shoot and murder 9 people (including your own fucking sister) in a shopping district. Another thing from this shooter was the lack of motive for killing everyone except for just having expressed an interest in killing people, no other motive other than that has come out yet.
Nothing about anything that I have just listed shows anything about being a leftist that could contribute to the shooting, maybe racial bias because 6/9 victims killed were black but that's a flimsy theory, but nothing about being a leftist at all could be the reasoning behind that. Maybe praising Satan could contribute though, I don't understand how Satanists operate and don't really feel like reading up on Satanism as a religion. Him being a leftist seems like a right-leaning talking point to show that "See leftists can do shootings too!!!!" or some shit like that, which should be obvious but like them being a leftist doesn't matter that's just like one random fun fact about the shooter. When it comes to right-leaning shooters, their ideology plays directly into the reason why they decided to shoot a bunch of innocent people.
In the end, we still have a White Supremacy, Gun, and Mental Health issue in the United States and they all need to be talked about, and fixed ASAP.