Now, I've used Airbnb a dozen times, but I can see the concern for people in the above situation. I've had people ask me when I'm renting certain Airbnb apartments if I live in the building, and they seemed a little upset with the idea of me just passing through for a week.
In case you haven't heard: http://en.wikipedia.org/wiki/Tragedy_of_the_commons
Also: there is a local law on the books, duly enacted by a democratic process, but you're arguing nobody needs to follow that law because you think nobody is being impacted? Is that your position? I have to assume you're an AirBnB host, so I wonder if you've contacted every one of your neighbors to see if they're cool with your gig.
Community can have many facets: security, friendship, socialization, child-raising, and even intangibles such as feeling integrated and belonging (not for everybody, but important to many).
Market stability is important for financial security, financial planning, schools for children, sense of home, reduced stress (not having to move often, or even needing to think about it).
Now, neither of these things is a resource per se, but I believe both are sought-after and generally preferred when people are given a choice. There are many laws and regulations made to help preserve these commons and prevent their erosion. For example, Prop. 13 in CA helps with financial stability in rising markets. Further, people actively work (invest effort) into maintaining these two commons and most people recognize that localities where either or both of these exist are more desirable.
Of course, that makes them also more desirable for investment property, and AirBnB facilitates the monetization of such investments, often to the point of enabling the investment altogether (the people who buy extra properties for the sole purpose of short-term rental). And I think it's pretty clear that those cases are profiting from the commons and not contributing anything back--net withdrawals that undermine the commons.
The "change is inevitable" argument gets tossed around for a lot of things, but often by the people who are profiting the most by change, and the faster things change, the more money they make. I think that in the domain of housing and community, fast change is disruptful to people. A landlord with 4 investment properties may think nothing of flipping them or kicking out tenants to remodel and rent on AirBnB, but the people involved have several months of stress and uncertainty in their lives, not to mention changing schools and sometimes jobs as a result.
I think city governments need to regulate AirBnB and the like so that the investment potential they create does not overwhelm the community and stability of residents. This applies anywhere the housing market is saturated or nearly so and visitors are plentiful: SF, Seattle, Portland, San Diego, Honolulu, and much of the east coast probably as well. I advocate for an annual limit of 30-40 day short-term rental for any given residential property. That covers the situation where you go on vacation and rent out your house/flat, and where there's a convention/concert in town and all regular hotels are booked (and you have a spare bedroom to rent). The booking site should enforce this limit and collect all hotel and sales taxes on the transaction.
My take on neighbors has always been that while it's good to know and like them, it's not required. A property being a discreet rental (as AirBnBs tend to be) would have neutral impact I'd argue. Other than seeing different people come and go, I would hardly notice that the property is anything but occupied. There is always the chance that someone unsavory would rent the property, but there's an equal likelihood (from my point of view) that a property would be purchased or long-term rented by someone of the same nature. I guess, frankly, I don't really care who lives next to me, since I do what I must to feel secure in my place.
I also think there's a bit of irony in your statement that change is championed those who are profiting, when you then lobby for regulation in the form of taxation. Instead of the purely capitalistic model of rewarding innovation and ingenuity, we give money back to the government to regulate something that may or may not need regulating in the first place. But I hesitate to go further, lest this turns to a political debate.
I just want to make sure you understand that I do get your point of affecting the feel of a community and the things that come with it, but I think that is highly subjective, and I'd even say that folks who look for that kind of experience in a living situation wouldn't be the kind to list their home on AirBnB anyway, and wouldn't sell to a flipper or someone who would.
In a sense you are right that "democratic" doesn't necessarily mean just or morally good, but I don't think you can compare what are essentially civil rights with property rights. I agree that laws should be backed with arguments about why they are needed and beneficial--though you realize it's not always possible to go into such details when I'm already so far off topic :-)
So here is my quick defense of SF's banning of short-term rentals (essentially making all AirBnB rentals in SF illegal): Regulating property is about zoning and controlling the market so that financial forces don't overwhelm the people involved. It is the city's responsibility to keep the city livable for its residents. This regulation defends local communities and avoids the instability of speculation properties, evictions for AirBnB conversions, etc.
Note that I think the total ban is both slightly too strict and probably expensive to enforce. That's why I advocate for a new policy: allow any owner (and renter) to do short-term sublets up to a limit of 30-40 days per year. For renters, they are limited to collecting the full amount of their rent in any calendar month, and any additional money collected belongs to the landlord. And finally, any 3rd party booking service must enforce these limits, collect hotel and sales tax, and turn records over to the city. That way people (even renters) can rent out when they go on vacation or make a little extra money, the city gets an elastic supply of rooms for big conventions, concerts, and sports events, but residential stays residential the other 330 days of the year and housing doesn't get bought up by speculators, nor does it have a bubble due to the value of AirBnB conversion.