If you actually have a group of peers that consistently challenge each other and have scholarly debate, congrats. You're in a very small minority. You personally not having a use for arguing online doesn't mean it's useless. I know plenty of Americans who have been convinced that gun control is important by things they've seen online.

Very few people in this thread are kidding around. It's worth pointing out that most of the things they are saying are extremely shallow.

Why should you only have discussions with people you know?

If you only have these discussions with people you know, more than likely, they are in your ideological bubble. You are just creating your own echo chamber. We may be randos on the internet, but we could be next to you on the subway or your cubicle. Most of us here probably like to debate somewhat.