> But if you want to do that at age 40, it's super likely that it's not by choice. And that's not something we ought to necessarily allow
If you mandate luxury in housing, everyone who cannot afford that level of luxury will go without housing -- or will end up in illegal and unsafe sublets with abusive landlords, which is far worse than an apartment of one's own that happens to have a floor area that is below your idea of luxury.
Replace 'luxury' by 'standards', among which size, but also fire hazard standards, noise standards, pollution, accessibility, height etc, and you can see why it's silly to take this libertarian idea to the extreme.
You have to find a balance. That balance will differ from city to city. But to mandate some minimum living standard makes a lot of sense. Breaking the law is not free of consequences, illegality is not the norm, it's a strong disincentive for anyone to engage in a housing practice which we as a society deem unacceptable. A line has to be drawn somewhere. From there you can, as a government, implement programs to help people meet those standards, and provide sufficient resources to do so.
Whether you think the line should be at 3m2, or 15m2, or 50m2, you can argue. What society deems acceptable is up for debate. I fully agree there. But the notion no mandated 'luxury', or minimum standard, should be set, and for government to just allow anything, without standards, because hey, otherwise you might create a situation where almost everyone lives according to an acceptable standard, except for a few edge cases temporarily breaking the standard illegally... I think that's silly.
If you mandate luxury in housing, everyone who cannot afford that level of luxury will go without housing -- or will end up in illegal and unsafe sublets with abusive landlords, which is far worse than an apartment of one's own that happens to have a floor area that is below your idea of luxury.