> Also, if putative negative effects from social media exposure were as strong and unambiguous as lung cancer in smokers, we wouldn't be having this discussion.

This is not necessarily true. Lung cancer was rare before cigarettes. Research had already revealed cigarettes to cause lung cancer in the 1940s and 1950s. Even so, in 1960, only 1/3 of doctors believed that cigarettes caused cancer. This was largely due to the tobacco industry's denialist propaganda. Even as late as 1972, the tobacco industry was putting out propaganda that was having a noticeable effect on teens and young adults. So, even with the "strong and unambiguous" negative effects of cigarettes, it still took 25+ years for most of the US population to accept that cigarettes are bad.

That was the tail end of tobacco's supremacy, but look back to where it started. When explorers found it being cultivated and used medicinally in the New World, it soon became one of the largest cash crops here.

Tobacco was exported to the rest of the world, became a hot commodity for vast plantations, creating a huge labor market (which was filled with enslaved people), and built wealth for many Americans.

Tobacco shaped the Americas as we know them today, and our history would be completely different if it weren't for that industry. And bringing up lung cancer, and expanded diagnoses, and expanded detection, is miniscule in the scope of things, because everyone knew it was a psychoactive drug, everyone knew that smoke makes you cough and clogs everything with gunk, but it had been worth its weight in gold. (Not to mention its gradual adulteration and dilution into something unrecognizable from 500 years ago.)

There's another term of art: "social communication", which encompasses radio, television, and Internet modes such as email and instant message. So we can discuss 'social media' as a specific phenomenon, or we can discuss its niche in the longer history of social communications. It is a morally neutral thing for humans to communicate with one another, but, if the medium is the m[ae]ssage, then the mode of communication will shape how it's composed, sent, received and absorbed.

We would not be having this discussion because the metaanalysis would have been unambiguous.

I would argue that negative effects from social media must be expected to be much harder to detect, because they would/could only manifest in changed behavior (possibly long-term!), and given how pervasive social media has become there is not even a good baseline for studies.

Picture e.g. social media exposure having a long-term negative effect on ability to focus, motivation to learn/work/self-improve and general satisfaction/self-image/outlook-- these are all somewhat plausible, and could be extremely difficult to isolate in studies.

Regarding smoking in particular: Imagine there being absolutely zero cancer/physical health effects, everything else being exactly equal. Would that make it okay to you? Because to me, it absolutely would NOT-- a society that allows under-age persons to become strongly addicted to something, handing corporations a convenient metaphorical straw to suck money out of them for the rest of their lives-- that is a society that has failed their offspring, to me. And social media (give its addictiveness and value extraction via ads etc.), is basically in exactly that situation already.