I do sometimes, although nothing he can see.
> Why should I be telling my child not to do something that everyone around him is doing
Me doing something isn't the same as "everyone around him".
If you refactor that to reflect reality, you get "Why should I be telling my child not to do something that I am doing?"
Then my answer is: they're a child. Not an adult. I don't let my son drive, even though I can. I work; he goes to school. I drink alcohol; he doesn't. I'm on social media; he's not. I'm married; he's not. I watch horror movies; he doesn't. Brains fully develop by 25. My son is now 7. He isn't just a smaller version of me. He's a child version of me.
Yes. I don't drink much, once or twice a month, but if we're all round someone else's house I may have a beer in my hand.
As a kid I hated when adults were drinking alcohol in my presence. They got even louder and dumber than usual after drinking.
My mother has always been laughing stupidly with a single glass of wine, my father could drink 3 before you notice. Same when I am not drinking and my partner have a beer. She won't speak louder or do act differently after 1 or 2 light beers. But in her case the line is really thin between the virtually unnoticeable state, the moment you realize she should stop drinking and the moment she is completely wasted or start feeling bad, especially if the drinks are stronger. On other people it is more gradual.
My point was a bit unrelated to all this, so I'm just checking your original question's answered.
As an adult, I can always feel the pull of real life. If I keep watching YouTube or playing video games I know it's going to impact my job, wife, kid, etc. Some adults aren't even that good at regulating this, but I think kids are, on average, way worse about it. Many don't know real consequences or regrets for failing to manage their time.
Although I'll admit I do agree with your comment in the sense that I think I should stop using YouTube entirely. People are discussing how it can really mess with a kid's brain, and I don't feel like I'm immune as an adult. Yes, I have more discipline than a child, but this feels like it can be a cheap acknowledgement made as a rationalization, like a chainsmoker saying his lungs are stronger than a kid's, or an alcoholic saying the same of their liver.