I hope you're right but I think you're dead wrong. Social media has not only affected the mental health of millions of people negatively, it has brought about social, political and economic harms that will affect the planet for generations.
But also it doesn't have to exactly reproduce the harms of smoking. It could be that the effects are primarily present tense and completely gone if you stop the habit, and nevertheless, amount to a cumulative social harm that makes it a worthy analogy to smoking. Social media also doesn't cause secondhand smoke or stained teeth, or unpleasurable odors on your person or home or furniture. It doesn't leave butts or debris on the ground. There's probably a lot more I'm not thinking of either, but you can see how nitpicky that starts to feel.
Is there any reason to believe that "social media existing" is a worse and more enduring harm than tens of millions of people dying in the Second World War, the trauma of the survivors, the vast destruction of infrastructure,or the start of the risk of nuclear war?
Yet the post war baby boom seems to have led a remarkably fortunate life, overall.