Mostly single white male here. During my time here, I've had three friends with benefits. Two have absolutely no idea, neither seem to be interested in this type of a lifestyle. My most recent FWB has mentioned, in passing, she had a black boyfriend in the last few years. No talk about sex, so no idea what she thinks.
Another FWB showed a LOT of interest in this lifestyle, I would share interracial movies and GIFs with her, and she would say things like "I need a black dick, daddy". She knew I was on here, in that I mentioned I was on an interracial site, no idea if she ever looked at the site, though.
The first FWB, she had no idea. She is actually a little older than me, and is a touch racist, I think. I joked that I'd like to see her with a black guy, didn't get a positive response.
I have no intentions of telling friends or family that I am a member on a site like this.