It’s really more a case of liability. I don’t have much doubt that the mother of the shooter of the Newtown children would be found liable in a court of law for failing to keep her high-powered weapons stored safely from the mentally ill man living in her household.
Now, would the protestors for liable for the crimes that took place in Ferguson? I would argue not. Would Mr. Brown’s family be liable for those crimes? Well, with the exception of the stepfather who said “Let’s burn this place down” I would argue not. On the other hand, the stepfather’s words, well, that would make an interesting case.
On the liability insurance, why are you so sure it would be expensive? If these incidents are truly rare, then the cost would be minimal.