I stopped using Airbnb wholesale after experiencing very similar things to what the OP has described in this article.
Plus, hotels are just better.
Though they can directly address this by taking photos out of the mix. Interesting question: Right or wrong to make decisions about trusting strangers based on how they look? I know my answer, what's HNs?
Airbnb has chosen it's system (and refuses to address the flaws inherent in that system), so I've chosen not to use it.
There was a history of cab drivers in NYC refusing to pick up black customers - when Uber came to town one of the first questions was "can drivers see my photo", which they can't until they accept the ride IIRC. I don't see this situation as being too different.
You could, with mixed results, I'm sure. There are many other factors to base a prejudice on; for example "does their name /sound/ black?"
Airbnb could also establish an anti-discrimination policy, which if you are caught in these types of incidents, you and your properties will be banned for some amount of time.
I've never used the service, so I can't say for sure, but I can think of at least a few good ways to accomplish this along with a team responsible for checking into flagged events and user reports.