Rittenhouse was 17 at the time this occurred. If he were 18 I think that he'd have been legally entitled to open-carry his assault rifle.
>> What baffles me more is that not one single responsible adult tried to stop him. In fact his own mother drove him there herself.
This doesn't strike me as baffling whatsoever - it's the current right-think inspired by the NRA, Fox News, et. all, and the hammered home-but untrue US versus them narrative sprinkled with numerous unfounded conspiracy theories.
Rittenhouse likely believes that he is a patriot standing up for American values against the abhorrent, Godless, criminal left, prone to vandalism and violence.