In practice, it's impossible to keep this from happening. If you don't construct luxury housing, it's not like you can keep people from moving in. Witness all

In practice, it's impossible to keep this from happening. If you don't construct luxury housing, it's not like you can keep people from moving in. Witness all the tech employees living in genuinely terrible Mission apartments. All that happens is you end up with gentrification that works around construction laws: old single-family homes being converted into hacker houses, run-down houses being rented by well-paid tech workers, with lower income people being forced to move ever further away. Objectively, most San Francisco housing is really not attractive. Yet rents are still extremely high because there is demand despite the poor housing. It makes far more sense to construct efficient luxury housing which can soak up the luxury demand so high-income earners don't end up taking over the traditionally affordable housing. Now that the construction pipeline is finally coming through, we're seeing this effect and rental prices are starting to fall. If your theory were true, we'd expect rents to be rising now that construction has finished—the exact opposite of what has happened. It might be possible to make an area unattractive for gentrification, but I think it's pretty damn hard. Construction bans certainly don't do it. Not even violence does (though crime as an affordable housing strategy is significantly under-researched).