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.

Just to be clear, to get to the definition of affordable (3 times medium family income) most detached homes in cities would need to lose 80-90% of their value.

Hey there's 2 of us.
I wouldn't care if my property stagnated or dropped in value if it meant people could afford a better life.
It only has said market value when I'm selling and I don't intend on selling, probably ever.

I'd rather have a young family as neighbors instead of some management company doing the bare minimum maintenance and let it slowly crumble while milking renters. It's a better community.

In a selfish roundabout way I've started giving a hand to the new renters nearby that I like and help them with small things that their landlord won't fix.

For many homeowners their home equity is their only remaining retirement plan.

Maybe you are fortunate enough not to be there but many are so any government that makes moves to reduce that equity will be gone the next election cycle.

Want a single detached house? Start climbing the property ladder in the middle of nowhere not presuming it’s realistic to start at the top in a major city anymore.

Hard truth gonna get downvoted. Pity.