Hell is not, strictly speaking, other people. But for a teenage girl, nine hours a day of other people evaluating your appearance and utterances as you attempt to negotiate their preferences and attitudes and jockey for some intangible sense of status is probably something very much like hell. Studies by Twenge and others have shown that depression is far more likely to be correlated with frequent social media use among girls than with boys, who in any case are more likely to use their devices to play video games. The first person I ever knew who “cut” was also the first acquaintance of mine to use a social media service of any kind (LiveJournal); she had gotten the idea from a YA novel called Cut, a lurid and almost romanticizing treatment of self-harm whose publication can only be defended as a kind of misguided attempts at raising awareness of a problem that has grown exponentially worse since it appeared in 2002.
Most adults do not have the luxury of deciding whether the way we live now is healthy. If you use a computer at work and your employer insists on being able to contact you at all hours, you have no choice but to keep your smartphone near you. This is not the case for children. There is no reason that a child at 10 — the average age at which an American now receives his or her own smartphone — needs to own one of these devices. The downside of waiting to give children these powerful tools designed for adults until they are emotionally mature enough to handle them is practically nil; the upside is, or should be, self-evident.