The law on housing discrimination is quite clear and even-handed on this topic - ad distributors are liable for discriminatory ads they publish (the law specifi

The law on housing discrimination is quite clear and even-handed on this topic - ad distributors are liable for discriminatory ads they publish (the law specifically includes "publishes" in the list of criminal verbs, and this was actually enforced in court against the New York Times in the 80s); and selectively-targeted ads are discriminatory (see Code of Federal Regulations section 109.25, down near the bottom of https://www.hud.gov/sites/documents/DOC_7781.PDF https://www.hud.gov/sites/documents/DOC_7781.PDF)