> The people chasing him were responding to what they thought was an active shooter situation
Even if we assume that they actually thought that, they attacked someone who they had no reason to believe was involved in said "active shooter situation." The most favorable interpretation is that they were vigilantes who attacked with deadly force.
If Rittenhouse had chased down someone you agreed with politically, claiming "an active shooter situation", you'd want his head.
There's a reason you don't see protests and hockey riots turning into gunfights north of the 49th. People don't bring guns to them, because they know that if they use them, they are going to get an absolute world of shit dumped on their heads by the courts.