I don’t disagree that the impulse which drove Rittenhouse was probably that of a vigilante. Vigilantism mostly occurs in settings where effective law enforcement is missing in action.
In the summer of 2020 following the death of George Floyd, Democrat mayors of many large cities instructed their police forces not to enforce the laws against mob violence, arson, property damage, and looting. The mayors’ apparent belief: the rioters were entitled to break the law because of their felt anger. Our law recognizes no such entitlement, no such holiday from lawful behavior.
With inner cities being burned and looted while police passively watched and did nothing, vigilantism was almost to be expected. Law-abiding people who don’t share the rioters sense of grievance are moved to interfere, to defend property as well as human safety.
That appears to have been Rittenhouse‘s motive. The blame rightly accrues to Kenosha’s mayor and/or city council for their cowardice in refusing to enforce the laws.