The number of wealthy people looking for a pied-à-terre in SF is not a fixed quantity. It seems to me that that number has grown significantly compared to, say, 10 years ago. And that that's mostly due to the increased prestige of the city (as perceived by that wealthy set). That prestige comes from economic growth, but also from a sense of how friendly the city is to pied-à-terres for wealthy people. So building more of them might just end up increasing the demand for them.
Sure, the process won't go on literally forever until the city is nothing but vacant luxury condos, but the total demand after that compounding effect has gone on a while may be much more than it appeared at first.
Thankfully, this not-fixed number is also not infinite. Just as the housing market also does not need to operate over a fixed quantity of housing. Building more increases that not-fixed quantity so that the not-fixed quantity of demand might be met.
When you have an economic boom, you need to grow your infrastructure to match. Not sit around bemoaning that that might enable future growth that will, to a great degree, happen even if you don't grow infrastructure.
Look no further than the current housing crisis - accurately predicted in 2000 - to see the results of the notion that growing infrastructure is bad because it encourages use of infrastructure.
There are exactly zero tricky debate tactics going on here.
There is a limited number of wealthy people looking for a San Francisco pied-à-terre, and that is a market that can be exhausted without driving all other residents out. At which point standard market forces mean construction for the less wealthy will occur.