Careful. There is no law that says you have to take affirmative measures to ensure that your housing ads reach all races equally, BUT it is illegal to INTENTIONALLY skew housing ads to disproportionately target, or avoid targeting, specific races. More info here [hud.gov]. So would it be illegal for someone advertising an apartment for rent to use Facebook's service? Maybe. If they were using it to ensure they were reaching all races equally, that would likely be legal. Otherwise, likely illegal. The same is true for ads for employment and credit. Other advertisers face no such restrictions.