People think gentrification is "evil" but they don't seem to think why people leave their old communities to begin with. By stopping gentrification you are unknowingly abandoning far more people by forcing them to stay in a bad area.

Gentrification is primarily a problem with the current system. I can easily imagine an economic system that decentralizes economic activity akin to Distributism which will make it easier to rebuild and improve run down communities without having to move somewhere else.