It seems like your response is "AirBnB has no moral obligation to try to discourage its hosts from violating an agreement it knows likely exists", but I'm curious as to why you chose to throw this back to me as a question rather than stating a concrete opinion. Do you hold other companies to this same standard, and are you comfortable stating on record that what's good for the goose is always good for the gander? If so, why disguise your opinion as a question?
On the point of corporate morality, I'd note that companies in certain industries are frequently lambasted for acting amorally. Just look in finance. Big banks, mortgage lenders, hedge funds, high frequency traders. They face almost constant criticism for engaging in behavior or failing to prevent behavior, even when their actions do not violate the letter of the law.
Are there no AirBnB supporters who have criticized other companies for amoral behavior?