That is an interesting point, kind of on the edge I guess. If Facebook really wanted to do the right thing while allowing this kind of multi-targeting, they should then build something such as segments in the same campaign.
You want to target only a specific group that, under the law, can't be targeted/avoided? Fine, but then you have to create at least 3 segments on this ad to target at least 3 different groups, to prove that you are not discriminating.
A segment would be a version of the ad (design, copy, etc) + targeted group.
edit: my point here is that it should be Facebook's responsibility to make it difficult for publisher to post illegal ads, not the other way around.
You want to target only a specific group that, under the law, can't be targeted/avoided? Fine, but then you have to create at least 3 segments on this ad to target at least 3 different groups, to prove that you are not discriminating.
A segment would be a version of the ad (design, copy, etc) + targeted group.
edit: my point here is that it should be Facebook's responsibility to make it difficult for publisher to post illegal ads, not the other way around.