The obvious point is that Facebook cannot provide accurate review-and-takedown of the total activity of billions of users. It doesn't matter what you legislate, it's currently not possible.

Given which, "penalties for fake news" means one of: "after reports, which is too late", "all of it, so shut down your company", or "anything which annoys us enough to prosecute, so be proactive about pushing our stance". Choice three seems to be the usual outcome.