I don't know if this is really a tractable problem. At the end of the day, either airbnb lets hosts decide who stays or doesn't. If they don't let hosts decide, they'll likely lose a ton of hosts, since having someone stay in your home is a very personal thing and a huge risk. If they do, then they're going to have significant discrimination problems as long as people are discriminatory, i.e., basically forever.
I'm Indian and smell of curry (probably... at least a few times a month). If someone hates the smell of curry, they should be allowed to blanket disallow Indians from staying.