Gentrification: The process whereby the character of a poor urban area is changed by wealthier people moving in, improving housing, and attracting new businesses - typically displacing current inhabitants in the process.
In a nut shell, if a certain demographic is unable to maintain a clean, safe, and vibrant neighborhood, they are ousted by those who are able and willing. Isn't this how evolution works; survival of the fittest ?
The conditions of a neighborhood are mostly the result of the choices of the people who live there; not only income levels. If certain groups choose to embrace a culture which leads to rampant poverty, illiteracy, and crime, isn't it a good thing if that culture is displaced and eventually disillusioned to the point they abandon the attitudes which got them there in the first place ?