Also a new host, really unhappy, called, tweeted, filed feedback, and probably won't list until they fix this. The nice rep on the phone tried to walk me through turning off Instant Book (but the options aren't on my page), put me on hold for 5 minutes, came back with deep apologies, and subsequently sent an email with a link to a feedback page with a drop down menu where you can choose Instant Book: https://www.airbnb.com/help/feedback?type=instantbook
Here's a thought, though:
Since as hosts we can cancel if they break the House Rules, what about this rule?
#1: YOU MUST CONTACT HOST BEFORE BOOKING. AirBnB will not let us turn of the Instant Book feature at this time.