Well, the impact is variable, though. If people are buying pied-à-terres out of the existing housing stock anyway, consolidating them into new luxury condos downtown makes those apartments available to regular renters.
Even if some new luxury apartments are pied-à-terres which would not be in SF in the absence of new construction, if some are actually occupied then rents for the city in general will also benefit. (New downtown high-rises with super-fancy penthouses can easily have many real residents on the lower floors.)
Even if some new luxury apartments are pied-à-terres which would not be in SF in the absence of new construction, if some are actually occupied then rents for the city in general will also benefit. (New downtown high-rises with super-fancy penthouses can easily have many real residents on the lower floors.)