it's obviously okay for an individual to refuse to have sex for any reason but how about maybe it's also not cool to have a big double-entendre sign out the front of your brothel that says "NO ASIANS MAY ENTER"
this is getting complicated very quickly
There are tons of personal ads that say no blacks or something like no fat people. And they already split into women, trans, and male escorts too for certain clients.
Free association involves choices that are personal and can include many aspects (age, height, income status, occupation, appearance, etc)