I thought that Facebook's stance was that it was a platform not a publisher? If you have no editorial oversight or opinion on the content you publish (cf. not taking down known false political advertising) can you then claim "free speech"?
They didn’t. They ruled corporations don’t have much free speech when it comes to product advertising and declarations of potential harm their products may cause their users.
Can you post a link to RCT-based evidence backing this claim? I don't see anything on CDC website or any professional medical organization about Facebook being as harmful as cigarettes.