Thing is, keeping children out of Instagram, Facebook, or whatever new social media is hyping currently will probably make them kind of weirdos in their bubble, e.g. in school. At least this would be my fear (don't have children). And good luck trying to use any of these ad-infested privacy-invading platforms while trying to avoid ads.
Being an outlier when the in-group is actively having their brains turned to mush seems like the better of the two outcomes.
This argument is popular but doesn't hold water. If we suppose for the sake of argument that social media is bad for kids, then it is a parent's duty to keep them off it even if that makes the kid unpopular. As an analogy, consider a kid whose social circle is all shooting heroin. Would it then become acceptable to let your kid do heroin? Of course not. Similarly, even if all the other kids are on social media, it doesn't become acceptable to let your kid use social media (going with the assumed premise that it's bad for them).
It doesn't have to make them weird, especially if you're in a school district where there are no-phone policies. Otherwise it can be difficult, for sure.
Learning how to stand on your own in school is good practice for doing the same thing in life. By which I’m absolutely not saying “don’t have friends” but rather, you don’t have to be like everyone else.
My kids won’t be on social media until they’re not kids anymore. If none of us take a stand, nothing ever changes.