The harm is from designing them to be addictive. Anything intentionally designed to be addictive is harmful. You’re basically hacking people’s brains by exploiting failure modes of the dopamine system.

If I remember correctly, other research has shown that it's not just the addictive piece. The social comparison piece is a big cause, especially for teenagers. This means Instagram, for example, which is highly visual and includes friends and friends-of-fiends, would have a worse effect than, say, Reddit.

What about it being addictive by its nature? I find myself spending too much time on HN and there’s no algorithm driving content to me specifically.