Moral panic. Each generation does it to the next one.
Many of our parents (or those of us who are parents) didn't have access to TV / video games / computers / Internet from the moment they got home from school. Their parents probably wanted to restrict how TV was bad for them, and the previous generation probably was told they listened to the radio too much. Or that reading too much will make you weak...and so forth. With retirement or careers that allow for more "down time", there's a lot more idle time wasted on the junk we see on the internet...but are we focusing on a small percentage of retirees? Some have nothing to do (and have limited funds), others have plenty to do and want to things that get them accomplishing goals.
But I do get mentally languid on days where I'm on the internet or computer too much, instead of getting more work done. I rarely watch much TV, let alone more than one movie every other weekend, and have limited interest in video games in the last 15 years; I find them all uncreative activities with nothing to really show for after I've consumed them. There's plenty of studies that show that wrapping yourself up in too many daily hours into any passive activity isn't terribly good for you, so hopefully you're making some good money by doing it. Everyone is going to be a little different in that regard, but most people will not accept that they spend too much time on any one (or more) activity because we always justify that "someone else is worse" or "if I spent more time on X, I'll be happier/more fulfilled." And that's a trap we set up for ourselves...especially for an activity that's seemingly never-ending or just ends anticlimactically with only a temporary satisfaction to show for it.
I also came from a household where we only were allowed about one hour of TV per day, not including watching the news as a family. On rainy days/weekends, we were allowed a little more. So between homework, chores, physical activity, creative activities, reading, and other curious endeavors there wasn't a lot of need (or time) to do a lot of so-called "brain rotting" activity. Going back 25-40 years ago, there wasn't much of any way for a teenager to monetize technological endeavors other than software programming; nobody was making a living off video gaming. The internet was mostly supported by donated time and funds because there wasn't much money to be made off of it in the early days.
tl;dr If you want to do or be someone different, and you're spending too much time on something which is holding you back, that's what's rotting you. If not, then carry on...
