As others have said, watching 4 hours of anything might be problematic.

However, my point is this: different things require different amounts of moderation. Candy all day is probably worse than carrots all day. In moderation, candy is great. Same as YouTube.

I would say no, the point is that there's _nothing_ that's good to be watched for 4 hours

Something like Sesame Street might be good. My problem with YouTube is it creates feedback loops where if you like something you seek out more of it, but with a near infinite range of topics. Throw an underdeveloped mind in there who is using basic stimulus to work out what is good and bad and who knows what will happen.

Wouldn't surprise me if that feedback loop was damaging even for many adults, but at least they are responsible and already have some grasp of how the world should work.