I've traveled & stayed in Airbnbs quite a bit and have met the full range of hosts: those just doing it for fun & to meet people, working to cover their rent, allowing themselves the freedom to cut down work and finish their book, work on their startup, bring their B&B business back after 1 bad trip advisor review, and on and on. These are honest, good people with a variety of motivations. I've never stayed with a host that is doing it to screw over their landlord, spite the hotel industry or trouble their neighbors. Similarly, we aren't crafting our product to damn the man - we are driven by the lives we are enhancing by existing.
Regarding opening a brothel, bar or club in their dwelling? Think of it this way: if your neighbor has parties, all of the activities of those establishments can/will happen. As far as neighbors go some will not care and others will. If it is degrading your quality of life or endangering your wellbeing - then talk to the person and explain your side, file a complaint or whatever it takes to feel safe again.
As a side note, I am not a host. As I signed the lease my landlord said "I know you work for Airbnb and it's unfortunately not allowed in this building." I want to be host for a number of reasons but I've been told no, and that is fine. Though it is certainly a bummer.