They should react to it and they have. Most of their victories against racism have been obtained through non-violent means. I can't think of any that have been the result of rioting, violence, and looting. Can you?
Anger doesn't require violence and criminality to be expressed.
If people believe their rights are being repressed, compromised, or violated, by governmental institutions, it is never acceptable to respond in ways that violate the rights of other citizens.
The people of Charlotte (irrespective of the color of their skin) have a right to walk down the Uptown streets without being confronted by overly aggressive demonstrators who scream, curse, spit and threaten them. They have a right to do so with being injured or killed. The owners of the looted and damaged stores had property rights that were clearly violated. Many of the peaceful demonstrators left as soon as the thugs and agitators showed up and so their right of assembly was compromised.
The legitimacy of one's demand for rights disappears when part of the demand involves depriving fellow citizens of their rights.
When a group of citizens feel that they are at such risk or under such oppression that they have no choice but to rebel, sometimes they will.
Once they do though they are engaged in a rebellion, not a demonstration, and it would be ridiculous for the rebels to demand their rights from the government they seek to overthrow or break free of, if their means involved violence.
African-Americans are not engaged in a rebellion and the vast majority of them do not condone violence as a means to confront the problem they are very concerned about. The thugs and anarchists that have set fires, looted stores and targeted and injured police and white citizens are not engaged in a legitimate response to those concerns.
What is the political statement made by looting a store? How about trying to drag an injured reporter into a fire that was set in the street? Then there's shooting someone in the head or beating up an innocent civilian in a parking lot? What's that political statement?
Its criminality, terrorism, or rebellion.
For most of the local thugs who participate in the riots it's all about criminal opportunism. For the out of town professional agitators, it's criminal as well, but it's also as close to terrorism or rebellion as I ever want to see on our streets.
Understanding why many African-Americans are concerned and angry over what they perceive to be open season by cops on members of their community is not the same as justifying, in any way, the violence that has been going on for the last three nights in Charlotte.
The same understanding is not the same as justifying or participating in rushes to judgment, ignoring actual evidence, and spreading disinformation about an incident (e.g. "Hands Up! Don't Shoot!")