Yes, some teens are creative with uploading videos, most are not. But teens can still be creative with a smart phone, just don’t post that stuff on social media.
There were pedophiles, porn, extreme gore, cults, scams and a primitive notion of brainrot. Music and games (not that I played games, but honestly my mum thought that this is why I liked computers and what I was doing) were generally thought to turn kids into killers.
Computer users even in the best conditions (and not children) were looked at negatively- as if they were no life losers. The techbro thing, and the normalisation of computer use is a very modern notion.
FWIW I had the same exact situation as the parent, and heard it all from my mum. The computer was considered undesirable at best and actively harmful at worst.
My point is: on a societal level, the numbers are pretty clear that teens consume too much media (and social media is even more addictive) and their skills and attention span deteriorate.
The “computers were considered dangerous” means that people generally thought they were dangerous, especially to children.