I don't get the airbnb thing... Venice had almost no permanent residents since... 1992, long before internet was widely used. It's just an incredibly attractive destination. Before AirBnb people were renting their apartments to become jewelry shops, touristy bakeries and souvenir "balconies". As far as I remember Venice (since 30 years) it was the type of place where finding a local was equivalent to winning the lottery.
Tourists love it (for one thing, it makes spending the night IN Venice and not its satellite villages affordable to more people, not just the elite that can pay the ultra expensive hotels), owners like it... who doesn't? The elite that does not need tourist money and some visitors who (like me) complain that it's just a touristy fairytale illusion. Well, don;t visit it then. But there's nothing unethical about something that both owners and tourists benefit from. As for the "heartless" invaders the sign complains about, who judges what's heartless and what is not? Maybe the locals who sold their properties are equally heartless?
Especially in the case of Cuba, AirBnb did not cause any changes. Anyone who wanted to rent the flat did so, after complying with the laws. The one change I see many home owners stressing is that now they can market their product to a broader public. Those who are not that centrally located have found a market and -most importantly- the need for a jinetero to bring in tourists has now disappeared for the most part, a relief to both visitors and owners. Visitors know what to expect in a house, don't spend hours roaming around or being dragged by shady types who in many cases blackmailed casa owners too. I don't see Airbnb doing anything different than all those e-platforms did before AirBnb and continued doing. If I were a casa owner, I'd be very happy to have another efficient tool in my hands.