Instant Book is a deal-breaker for me, and I am very disappointed to see the vast majority of search results on the first several pages are IB. It is not good for Airbnb to prioritize quantity or quality, IMHO!
It isn't about discrimination, it is about ensuring the right "fit" for my guests and my space.
For example, a lot of people do not look at the map or read my descriptions. They see "Superhost", "Denver", and my great prices, and request based on those factors alone. Consequently, almost all of my non-5-star-reviews came from people who thought they were staying in downtown Denver, when I am actually 30 minutes away (though still a Denver address, which I cannot change).
After being burned a couple times, part of my process is to ensure guests know where my home is before I accept them. I don't see how I can maintain the same quality control with Instant Book.