And we see that every single day on Facebook and Twitter. Its against their terms of service, just like its against Parler's.
As a single entity, I don't really give a shit about Parler. What I do give a shit about is treating everyone fairly. If Parler goes because it has a shitton of users and can't swiftly police all content, then Facebook needs to go because they have a child pornography problem.
Listen to this podcast if you want to learn just how widespread the issue is: https://samharris.org/podcasts/213-worst-epidemic/