I assure you a 99th percentile in 100 m dash may have believed that smoking did not affect them the same way it does an average person, but they would be wrong. And so are you about your AI usage.
There's simply no reason to even draw a weak analogy to smoking. You'd do much better to draw an analogy to e.g. methylphenidate or amphetamine, which certainly you can abuse and get addicted to, and might even be harmful for the average person (even carrying the possibility of psychosis!), but which carry cognitive benefits with minimal side effects for others.
I'll give another concrete use: the other day I scanned a storybook with my phone and had codex OCR it and compare with a list I've started of words and sound patterns my kid knows how to read so that it could identify irregular words or new sounds for us to go over before we start the story.
Please, concretely, let me know what the adverse effects were there.
We do know that LLMs can cause psychosis, we do know it can cause people to behave in an unhealthy manner, etc. We are seeing more and more evidence that AI usages in education is at least correlated with bad grades. We are seeing people exhibit addictive behavior around AI. There is plenty of reasons to suspect that as we gather more evidence that they will become conclusive about the addictiveness and the unhealthyness of these products. For me this is obvious.
Like the education effect is pretty obvious: most people will use it to cheat on their homework and avoid learning. Some people will use it to learn new topics or with more depth, and give them additional targeted probing questions to answer (basically, give them more homework). Average achievement will probably drop. The high achievers will probably do even better.
Boiling it down to "it harms your brain" when people are already telling you how to use it to learn more effectively is just silly. Most people are happy to rot their brains. They'll take any opportunity to do it. If you're an outlier, you're probably aware of that fact on some level, and it doesn't make sense for you to make decisions looking at the median who behave completely differently. You have to look at the mechanisms behind the data and interpret under what situations they could plausibly apply to you.
The evidence were all pointing towards tobacco being both addictive and unhealthy, but it still took two decades for the evidence to become clear and public health experts to be proven right. Maybe in two decades I will be proven wrong and you will be proven right, but I doubt it. When the evidence are all pointing in one direction, it is usually because they are right.
Aren't most of these true of amphetamines/methylphenidate also, though? Except the "bad grades" part. Certainly Adderall is habit-forming for some people and has risks for abuse, just like it can contribute to mental breakdowns and psychosis.
Likewise, the psychosis-LLM link is incredibly rare.
It kinda looks like you're overstating the evidence. This is not a good comparison to 1950s tobacco -- by the 1950s, the scientific evidence for tobacco being unhealthy was already quite substantial. The problem was getting that information to the public in the midst of a disinformation campaign. Here, for contrast, the evidence that moderate LLM use in professional settings has overall negative impacts is still pretty light.
I only use LLMs rarely, and I don't have any kind of emotional ties to the issue. I just think your claims extend decently far beyond the evidence.