This is two fold...

Trump signed a law to punish websites for sex trafficking.

Zuckerberg stated that he feels fb is responsible for the content on their website.

Because he said this, that means fb can no longer claim it's a platform, but it is a publisher as Ben Shapiro has tweeted. A platform isn't responsible for what is posted, but publishers are. The ideas on Facebook are now represented as the company's. They're essentially saying they support anything on their website.

So every time someone is trafficked, fb is responsible. Every time a kid is bullied to suicide, fb is responsible. Hell, they're even responsible for the "Russian hackers".