This whole thing was so predictable from the beginning. The left has for decades been accustomed to holding violent protests, burning things, assaulting people, damaging property, etc, with little or no repercussions. In fact, they have a sympathetic media that focuses more on their cause than their actions. This level of on-going and increasing violence, however, has finally caused a counter reaction. Property owners and innocent bystanders have realized that the official power structure is not going to protect them and they are starting to fight back. I said that it wouldn't be long before these thugs went after somebody that was armed and willing to defend himself, and people would die, and now it has. This won't stop here, either, because the violent protesters have no intention of stopping their violence and will only increase it because they still believe there are a lot of soft targets that won't fight back. The counter reaction will only increase, as it becomes ever more apparent that protection is not to be found. This only stops when the protesters stop being violent.
You can argue that this kid broke the law himself, that he should not have been on the streets with a rifle, but when the police are pulled back, who is going to enforce the laws that the kid broke? The flip side of the argument, of course, is that without the violent protesters in the streets, the kid would never have been walking around carrying an AR-15. Think of how foolish it is for the protesters to, on the one hand, scream that the police need to be defunded and disbanded, while on the other, want those same police to protect them from the inevitable results of their actions.