Setting aside the questions about material improvement (in the form of income, etc) which seem well addressed by others, this way of looking at the problem over

Setting aside the questions about material improvement (in the form of income, etc) which seem well addressed by others, this way of looking at the problem overlooks one of the most serious critiques of gentrification: it disrupts existing communities, forcing longtime residents into environments where they no longer feel a sense of belonging and ownership, and reduces cultural diversity. Another way of looking at the point: "gentrification" is more than just the arrival of affluent people to a previously poor neighborhood. "Gentrification" also refers to the cultural changes that come to a neighborhood as a result of an influx of more affluent residents. The latter can happen (infrequently) without the former. Of course, this doesn't mean that gentrification is necessarily bad. It may be that the improvements to safety, material wealth, etc. that often come with gentrification are worth the trade-off.