Never heard of this so looked it up. Dude had an argument with his ex while in a car, hit her a few times, she managed to escape, he drove into a parade some time later. The motive behind the attack is unknown. What does this have to do with the parent post?
So he was a right wing extremist who murdered several innocent people. The parent was saying that left wing extremist attacks aren't nearly as prolific.
Edit: on further thought, no motive for the attack was established. This seems more like an act of random violence fueled by rage, rather than an ideological attack.