1. Econ 101 supply-and-demand theory is helpful in discussing these issues, but don't rely on it exclusively. Instead, use a mix of data, simple theory, thought experiments, and references to more complex theories.
2. Always remind people that the price of an apartment is not fixed, and doesn't come built into its walls and floors.
3. Remind NIMBYs to think about the effect of new housing on whole regions, states, and the country itself, instead of just on one city or one neighborhood. If NIMBYs say they only care about one city or neighborhood, ask them why.
4. Ask NIMBYs what they think would be the result of destroying rich people's current residences.
5. Acknowledge that induced demand is a real thing, and think seriously about how new housing supply within a city changes the location decisions of people not currently living in that city.
6. NIMBYs care about the character of a city, so it's good to be able to paint a positive, enticing picture of what a city would look and feel like with more development.
...Imagine destroying a bunch of luxury apartments in SF. Just find the most expensive apartment buildings you can and demolish them.
What would happen to rents in SF if you did this? Would rents fall? Would rich people decide that SF hates them, and head for Seattle or the East Bay or Austin? Maybe. But maybe they would stay in SF, and go bid high prices for apartments currently occupied by the beleaguered working class. The landlords of those apartments, smelling profit, would find a way around anti-eviction laws, kick out the working-class people, and rent to the recently displaced rich. Those newly-displaced working-class people, having nowhere to live in SF, would move out of the city themselves, incurring all the costs and disruptions and stress of doing so.
If you think that demolishing luxury apartments would have this latter result, then you should also think that building more luxury apartments would do the opposite. Price should think long and hard about what would happen if SF started demolishing luxury apartments.
HT: Marginal Revolution