Online outlets have a specific exemption for user-created content (https://www.eff.org/issues/cda230/legal); print outlets do, indeed, have to pre-screen ads and that's worked very well.

Even for tech companies, that exemption is limited; Craigslist got an exemption, but Roommates.com didn't because of the level to which its platform actively encouraged discriminating on prohibited categories.

Facebook is even now being pursued by HUD over its own tools allowing housing ads to be targeted by race, gender, ZIP code, or disability. https://www.npr.org/2018/08/19/640002304/hud-hits-facebook-f...