My opinion is that people just aren't particularly intelligent beings, in general.
When we drive cars for example, oftentimes it's like technology develops faster than we know how to use it and we end up road raging and killing one another in vehicular accidents because we don't want to be 30 seconds late for work and hate being cut off. In a sense, much like a chimpanzee, people just haven't evolved at the rate that our technology has and we don't quite know how to use our tools.
And with guns, it's similar. It's like we don't really know, in a general sense, how to properly handle them, much less Rittenhouse who appears to be just a kid.
So you have this untrained kid and he has a pretty serious weapon. It's not a little handgun, it's a large, assault rifle that we might otherwise only see on a battlefield in Iraq. And not only does the kid not know how to handle his weapon, but the people around him don't know how to respond to it either. Trying to grab it out of his hand for example.
In order of responsibility, I would start by blaming A. the government for allowing a kid to carry an assault rifle around. Then I would blame B. Rittenhouse for making the decision to walk around like batman with an assault rifle in the middle of a riot, then id blame C. the mentally insane guy that tried to take away Rittenhouses weapon and then D. the kid who hit Rittenhouse with a skateboard in an additional effort to disarm a vigilante who shot a guy with a grocery bag.
Rittenhouse shot 3 people. Each with their own mindsets and ideas. If he didn't bring an assault rifle to a riot, none of this would have ever happened. And further, if the government would have regulated this issue and made it illegal to carry the weapon to begin with, then maybe Rittenhouse wouldn't have made the choices that ultimately resulted in these deaths. We don't live in Afghanistan. There just isn't any reason to have a combat style weapon like that in a residential or commercial town.