The upside of it
The last two times that I was looking for apartments, I made extensive use of Craig's List. I was looking at 1, 2, and 3 bedroom apartments, with 2's the expectation. So I was generally looking to move in with someone that I didn't know. I looked at quite a few places in person, and tons of places online. Sometimes I'd go to see a place and the prospective roommate(s) was weird in some way that made me think that I didn't want to live there, even though the place itself was good. A frustrating waste of time. A lot of times when looking at listings, I could tell that the apartment was not for me. Every once in a while, the listing would look really good, and then I'd see that the lister had put something like only "white people", or "no Asians". Thank goodness that they were able to put that stuff in their ads; if they hadn't I might have wound up seeing the place, liking it and thinking that they were normal, and moved in. Selfishly, I want racist people like that to be free to express their racism in (non-violent) acts and expressions; I want to know who these assholes are, so I can avoid them.