I know better than to waste time arguing with a doctrinaire libertarian.

Yet here you are arguing :-)

What is your definition of rent control working? There are some studies showing that rent control does work to minimise displacement of tenants [1] and that tenants seek more repairs [2], even more of lower income classes.

If you define as achieving market efficiency, maybe that's not the objective.

It's like unionising, it may make companies less market-efficient by giving more power and control to the workers. Rent control affects landlords by giving more power to tenants.

Building more houses, etc., is an orthogonal issue to rent control.

[1] http://www.socsci.uci.edu/~jkbrueck/course%20readings/gyourk...

[2] https://www.policylink.org/sites/default/files/RentControlMy...

What about the non-tenants who now cannot find a place to rent, because it's less profitable to build more apartments?

You could always [raise taxes and] subsidize apartment-building... the G.I. bill would like a word.

Government does plenty of things that are unprofitable for the benefit of all.

Switzerland has a pretty good policy for rent control and tenant housing [1].

This kind of policy needs to be a multipronged approach in policy to provide both new construction and long-term leases (usually 20 years).

[1] https://housingpolicytoolkit.oecd.org/www/CountryFiches/hous...