In concept Airbnb is fine. Renting out spare rooms, renting unused time on your holiday pad at Cape cod, all make complete sense. It's making more space available, at a cheaper rate, while maximizing utilisation, and return, on an existing asset.

Equally there's some place for buy-to-rent investing to exist. There is, and will always be, a segment of the population who cannot, or doesn't want to, buy and this segment rely on rental for housing. If there was no invest-to-rent then that segment would be homeless.

The problem happens when there's an imbalance. When there's too much Airbnb (like Barcelona), locals get squeezed out of their own city. Some supply is good, too much is bad.

The solution to this is regulation. By regulating supply (prioritize in-home, limited permits for others etc) one can balance the three markets such that ultimately everyone wins.