My experience with social media is minimal, so take all of this with a grain of salt.
I never really got into social media. I made a facebook account because my friends were on it and college was right around the corner, so I wanted to keep in touch with those going away. The thing is, PMs and group chats were very rare and there were few meaningful posts/updates/whatever. There were so many random quizzes, pics, and game/app advertisements invites that it felt meaningless. I also felt awkward declining friend requests from people I know, but was not friends with nor was interested in becoming friends with. So I just stopped using it. Finally bothered to delete my account earlier this year.
I believe the users of social media can reinforce both positive and negative behavior. There are so many good things that happened, and will continue to happen, because the average person can reach a wide audience. There are also so many people getting harassed on these platforms it really makes me wonder about humanity.
I also believe the social media platform itself can reinforce unhealthy behavior. By trying to give the user an experience they want, social media tends to create echo chambers. The user would need to seek out conflicting information on their own, which not everyone does. This not only allows other people to negatively influence the user, but also encourages the user to be a passive consumer of information. Not really knowing where it comes from, just expecting it to show up and framed in an agreeable way. If the user hasn't learned/isn't learning how to compromise, debate, and/or disagree in a healthy way, it can harm their development as a person.
Social media is also designed to be addictive. Some games are also designed this way, for transparency's sake. All those likes, follows, etc release dopamine and can train the brain to keep seeking those feelings and continue using the platform. This could also increase stress because, ultimately, the desired response (likes, positive reception, sympathy, backlash, etc) and the quantity isn't guaranteed. Repeatedly receiving undesirable outcomes could cause or reinforce things like low self esteem, depression, or aggressive behavior. This is more of a "worst case scenario" line of thinking and I doubt that most social media users experience this.
Basically, I don't believe it's just the users of social media that make it positive or negative, how the platform is designed can influence it's users.
Also, I agree with LDSman, the law has yet to catch up to technology.