What does "Ethnic Affinity" mean?

When you place an ad on Facebook. you can specify that the ad not be shown to those of a specified ethnic affinity. Facebook does this as "it’s important for advertisers to have the ability to both include and exclude groups as they test how their marketing performs." The problem is that you violate the Civil Rights Act of 1964 and the Fair Housing Act of 1968 because the ad can be used in a racist manner.