I can't speak to Parler as I never checked it (and can't now), but I just checked the Gab homepage and I encountered anti-vaxx, anti-Catholicism, QAnon, and election fraud nonsense. This is just the frontpage: no cherry-picking. There is nothing outright illegal on the homepage, but it's also not a good look to be honest.

Aside: Gab is horrible technically speaking; Firefox uses my full CPU :-/