I read that all weekend people in Ferguson looted. So what does that have anything to do with the Michael Brown shooting? Is it just an excuse to steal?

Anytime law enforcement resources are exhausted on one matter people will loot.

This is common during natural disasters (ex. Hurricane Katrina), economic turmoil, and general uproar among the population as we see in the Ferguson, MO incidents.

Yes. But not all of the protestors are stealing.