If there is a high-demand tourist location (like many parts of Spain) and tourists are more wealthy than locals (like many parts of Spain) then new housing stock will also be soaked up by AirBnBs. In this situation the "just build" argument means you have to build enough housing to house every single wealthy tourist that wants to come before you start seeing any relief to local housing issues. Not only does that mean locals have to wait thought, say, 10 years of construction before their issues are addressed, but in the mean time the tourism sector will have dominated the economy, which is not healty either.
The tourists do not have to be particularly wealthy. All they need is to afford a per-night/week fee that is a bit higher than average equivalent local long-term rent.
At 100€ per night, at 70% occupancy the equivalent monthly rent is ~2000€.
