The text of the law[0] is surprisingly clear that FB's acceptance of these ads is illegal (unless I'm missing something big).
As made applicable by section 3603 of this title and except as exempted by
sections 3603(b) and 3607 of this title, it shall be unlawful—
...
(c) To make, print, or publish, or cause to be made, printed, or published
any notice, statement, or advertisement, with respect to the sale or rental
of a dwelling that indicates any preference, limitation, or discrimination
based on race, color, religion, sex, handicap, familial status, or national
origin, or an intention to make any such preference, limitation, or
discrimination.
[0]
https://www.law.cornell.edu/uscode/text/42/3604#c
