They do have to still abide by the laws and they still can be sued for failing to do so. Sandy Hook truthers and those giving them a platform, for example, have been ordered cease and deist by the courts as well. When people get hurt, they then have grounds to sue and the courts can order them to stop as well. Facebook cannot kill as many people as they want, they can still be held liable for damages.
It is just a matter of time before the US has to catch up with other nation's privacy and disinformation laws, for example:
The mission of the Law Library of Congress is to provide authoritative legal research, reference and instruction services, and access to an unrivaled collection of U.S., foreign, comparative, and international law. To accomplish this mission, the Law Library has assembled a staff of experienced...
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It is just a matter of time though before we pretty much have international guidelines on this that most nations follow, we are just in that gap in between before they are created is all.