I don't think the problem is necessarily knowing what kind of place the world is, but being constantly reminded by it. I believe social media would be harmful even if it was full of happy news, simply because it provides constant distraction which isn't natural for our brains.

Also, often young people compare their lives to unrealistic images portrayed through social media influencers, and get depressed when their life seems worse. So even "positive" content can be a source of depression.