Much depends on how this is done. Don't forget that just because someone is in the National Guard that does not automatically make them any better then the street thugs all around them.
Katrina aftermath showed some on the police force in full uniform looting the stores.
Any way, the Guard would have to be retrained in the rules and regulations of the city's laws and human rights. Would they have the power to arrest, confiscate weapons, drugs, thieves,---how would the donut shops go about suppling free donuts and coffee for that number of hungry Guards men and woman.???
Bringing in the Guard would place everyone in fear especially the non criminal element. The stress of living under suspicion, trying to separate themselves from family members that may be wanted-----Pre-WW2 Germany comes to mind.
The Gangs will now have something to do, figure out how to outsmart the Guard, what a hoot when they steal the Guards transports. This could lead to the stop of gang fighting, they would all band together for a common cause.
This is the worse idea I have heard of in years, it gives me the creepy crawlies just thinking of what could go wrong.