With respects to cigarettes, I am open to being persuaded by the fact that an enormous amount of empirical data underscores the risk to an individual's health posed by the consumption of cigarettes and, therefore, it can be argued that a parent allowing their children to smoke could potentially amount to child endangerment or abuse, depending on the context. That said, I remember my parents caught me smoking and had me smoke an entire pack to induce illness so that I would not want to smoke again. And it worked. So this is a topic more complicated than it first appears surface-level.
With respects to social media, if we were to apply the same standard as we do with cigarettes and physical child endangerment then we are opening ourselves to the possibility that information and tools of communication can be "harmful" in and of themselves. As the article points out, this puts freedom of speech directly under attack. Freedom of speech is a fundamental human right and therefore it is part of the government's very mandate and "raison d'etre" to protect and defend it. Moral busy bodies and their moral panics be damned, and I say that even though I despise social media and wish it didn't exist. But just because I don't like something doesn't mean that I think it should be illegal.