Having read through lots of public comments in response to planning applications, I don't recall anyone opposing new housing because it would reduce the price of their house. For greenfield and greenbelt developments, people mention relevant planning policy..1/ https://twitter.com/JonnElledge/status/1274270564178448384

(e.g. Local Plan, Core Strategy, 5-year land supply, Site Allocations Document), the impact on habitats, wildlife, the countryside, the loss of agricultural land and sometimes flood risk. A common concern for both greenfield and brownfield is the impact of the extra housing.. 2/

on infrastructure and services: often there’s already a three-week wait for a routine GP appointment, schools are over-subscribed and roads congested. It’s easy to shout “NIMBY!” without acknowledging people’s legitimate concerns ...3/

about all these issues and the lack of investment in the infrastructure and services that current and future residents need. 4/