You can usually talk a person down enough to reason with them, but a mob just feeds on itself and you need to find a way to get everyones attention quickly. Waterhoses and tear gas only work if the crowd is small enough, a bigger mob calls for more drastic measures.
We don't use watercannon except in Northern Ireland. At present they just seem to be getting more police.
In the end dozens lost their lives, thousands were injured and hundreds of millions of dollars worth of peoples properties, in some cases their livleyhood, was destroyed. A lot of arrests were made but the majority of the pettier crime went unpunished.
This is mainly looting I think, no one has lost their lives.
It wasn't until Police, Marines and US Army National Guard took the the streets in force did the rioting end. Most rioters were intimidated enough by having assault rifles pointed at them by men in uniform to stop what they were doing.
There is a major issue with doing that. The army is not trained in riot control. Lets face it, the British Army doesn't have a great record with dealing with protesters. (And we are still having issues due to it)
Violence is never good but sometimes that is what is needed to appease the situation. People may not even need to be killed/shot (in fact I would bet on it) but if the army were to turn up with a few tanks and a few rifles most would run and hide under a rock.
As said above, the army are not trained in riot control. If a someone with a gun in their hand panics.. boom. 20 people dead.
Plus it sets a really bad precedent.