The issue is that of trust; if you have a full-time neighbor (renting or owning), you generally trust that they will respect the building/neighborhood, and over time will grow to trust them as people. They're more accountable. When you have random people flowing in and out every few days, that trust is not there. For example, Airbnb guests won't go out of their way to be sure to honor quiet hours... why bother if they're just there for a few days and don't have to deal with the neighbors on an ongoing basis?

I absolutely love using Airbnb and prefer it over hotels in nearly every place I visit, but I won't pretend it's somehow good for the neighborhood or neighbors.