Canada

I, for one, would not mind if my property value stagnated or decreased so that others could have a better life.

This is why you will never be in any decision making capacity.

IMO you aren't really a part of the problem if you support increasing density around you and policy that makes units an attractive option for the majority (improving public transport, amenities, minimum building standards such as sound proofing, floor-plan and storage space, HVAC, etc). You can't rely on individuals to voluntarily give up space they don't need any more than you can rely on them to voluntarily give up money they don't need. Any system which relies on discretionary kindness for the greater good is doomed to fail.

Most people don't choose detached housing because they need a backyard or extra space. They do it because it's a better cost-benefit when compared to the higher density housing stock. The solution is to make higher density the more attractive cost-benefit.