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.
This has everything to do with the parent comment’s insinuation that political extremism is only a one way street.
Also you conveniently left out the part where he murdered 6 people.
“He drove into a parade some time later.” Unreal.