It hurts us in many ways.
1. We instinctively become unhappy comparing our lives against all the ways others' lives seem to be going better, and often become more unhappy trying to maintain a false image of a great life.
2. We use social media as an attempt to feel connected without the emotional support of talking and touching, so spending hours online doesn't actually fulfill basic emotional needs, feeding depression.
3. Social media makes it easy to get trapped in a thought bubble where we never hear the other side, to the point the left wing can say "all the right wing are haters, they're evil, they should die!" or the right can say "all the left wing are crazy, they have nothing reasonable to say!" Then the middle ground erodes as the social divide deepens.
4. Social media mobs enable bullying in the name of justice.
Examples - the social justice warriors see it as appropriate to not only savage someone online for expressing an opinion they don't like but then get all their personal information and may spam the person's parents, call their employer to get them fired, try to destroy their relationships (like the SJWs harassing Sargon of Akkad's girlfriend because he posted a video they didn't like).
Or a private religious school near us that teaches traditional marriage and said to avoid conflict for students and community, they wouldn't admit children of homosexuals. That story went national, and the school received death threats to teachers and administrators, suspicious packages, threats to burn down the school. I wonder about the thought bubble someone is in that the idea that threatening to burn down a school with 200 children inside to punish the haters is not considered hateful in itself, much less pointed out as illegal.