No one is investing in those sections of the cities right now.
The huge crime rates in those areas is WHY no one is investing there.
Crime will drive potential businesses, services, etc., out of an area, and keep them out of a particular area, a LOT faster than a strong police presence.
Granted. Nobody wants nightly breakins by crackheads, either, or stray rounds from gangstas coming through their window.
I just think that such restrictions on movements would be the proverbial nail in the coffin, preventing even the demolition and gentrification that's overhauling such areas elsewhere. Miami is a very good example...as real estate prices go higher and higher, development of new offices and housing is pushing further and further from the beach and downtown, and that means that
A) the warzones get bulldozed and
B) the decent people owning houses there, after decades of zero sell value, can seriously cash in on property values because the developers want it, and even
C) people who outright own a business like a landmark restaurant will have a prosperous clientele coming in without fear of venturing into a bad area. (This has happened, too! Lots of formerly inaccessible 'soul food' and Cuban cusine places are doing very well!) And thus the area is renewed.
Actually, it's sort of a return, at that. When Overtown was new, it was heavily African-American, but safe. People of all races would come there to see Count Basie, Ella Fitzgerald, Cab Calloway, Nat King Cole, Aretha Franklin and the like performing in theaters long shuttered.