I totally agree, service fee is way too high. Guests do complain, because people are now used to online services that only charge minimum or no fee for simply using the booking service. I understand that running expenses for Airb&b may be higher than, say, Craigslist, but that doesn't justify how high service fees are on most bookings. Most puzzling, the longer you stay, the more you pay in service fees, which to me doesn't make sense because running costs for the website should be identical, no matter how many days you book.
I for one, if the final price turns out to be similar, would rather give my "service" money to an hotel, at least they are offering employment to more people.