Transparency

There are two answers to this criticism, which as far as I can tell the millenials have yet to bother offering. (They are too busy fraternizing with one another, like mayflies enjoying the sunshine while they can -- and good on them.) The first is that all this public exposure causes an inflation of the outre. Holding a big red plastic cup in one hand and a bottle of cheap vodka in another? Not to worry! Everyone's doing it, and by the time these kids grow up, everyone will have done it, and most everyone will have documented having done it.

The second answer is a little more interesting. Transparency in one's personal doings and thinkings is what gives the world a chance to offer feedback to the individual. This is closely related to the notion that if you want something unusual, and you don't ask for it, you are very unlikely to receive it. If some grownup liked to party when he was a kid, and documented it on FaceBook, well, I guess his colleagues will know what type of stories to share with him at the annual company picnic. On the other hand, if some other kid posted lots of pictures of his homemade chainmail on a Society for Creative Anachronism forum, his colleagues will know he was (and likely is) a very different sort of being than the vodka drinker.

Transparency lets us aggregate more accurately and efficiently.

The ones who aren't transparent are fearful. They're either doing something so deviant that it can't be shared; or they're conformists who just want to fit in. In both cases, their opacity is a product of the fear of being discovered for who they really are. (There's also the possibility that they just don't participate in Facebook or whatever, but the kind of transparency I'm discussing here extends into Real Life as well.)

As we gain confidence in our abilities and achievements and potential, we can become more and more transparent. And this produces a positive feedback loop: the more transparent we are, the more information we give the world about how best to position us in its vast edifice of possibilities. And then we succeed better in the world, and gain more confidence in our abilities and achievements.

Maybe these seemingly exhibitionist millenials just have enough confidence (or naivete) to act as though the world will treat them kindly given who they are; and they proceed apace, mayflies in the sun.