If the rate of visitors reaches a rate where where the occupancy rate of airbnbs is makes them less interesting than long term units, congratulations, you have found market equilibrium.
You make a weird argument: you mention the people that work in the city and want to live near it, and this argument has at least 2 flaws. The first one is that in a numbers game, the people that lose out on this exchange is a much smaller number than all the rest. That is, a small proportion of people see their conditions relatively worse because of how a third party does with their property. IF you put it up to a vote of all people involved, they would lose out big time.
The second is that you dont take into consideration that airbnb has made it cheaper and easier to travel for people of that socio-economic status as well. Its not only hipsters and software engineers that user airbnb. You have to weigh in the benefit of the consumer.
Do you have any sort of data to back up your claim that there are no empty properties?