Final answer:
Gentrification is controversial due to the displacement of lower-income residents, the tension between economic development and community preservation, and the various forces that drive the phenomenon such as economic interest, cultural trends, and government policies.
Step-by-step explanation:
Gentrification is controversial because it involves the transformation of urban neighborhoods, often leading to displacement of lower-income residents. Although gentrification can bring economic development and renewal to deteriorating areas, it often results in increased rent and cost of living, which can force existing residents and businesses to relocate. The process can exacerbate social and economic divides, sometimes leading to tension and conflict as seen in events like the Tompkin's Square Park Riot.