Social is the weapons-grade plutonium of online design; you can use it as part of a stable fuel source, or as the components of a weapon, but it's most likely to end up carelessly scattered around your community poisoning it for generations to come.
In Instagram's case, its social enablement is relatively anodyne, but it illustrates some common problems: comments are higher-bandwidth than content, and comments are easier to create than content. Thus, low-value information is added to the system at a much higher rate than high-value content. Solving this is, to put it mildly, not easy.
That right there is sheer genius, ladies & gentlemen!
It's interesting to compare sites with healthy social components (e.g. HN & reddit), to those whose social component has died off (e.g. /.), to those which use it unhealthily, if profitably (Instagram?).
What makes a social component healthy/unhealthy? I generally found myself nodding to posts until I read yours, which made me think quite a bit harder. Can a community with questionable moral value (neo nazis) have a healthy social community? I certainly think those two are not mutually exclusive, and to tie them together may detract from a complete understanding of what "unhealthy" means.
(To answer the question myself, "healthy" vs "unhealthy" in my eyes is whether the community is a self perpetuating echo chamber, (for which many parts of instagram this certainly holds true, content regurgitation and mindless browsing, but I'm apt to believe not ALL of it) and similarly an ISIS forum may have more of a tendancy towards "unhealthy" social content, I don't believe it necessarily dictates it; I've read some fascinating discussions even on HN (linked to other sites) between extremist Muslim/European religious experts that would be a fit for the most cultured discussion boards, even if context of one sides subject matter is far darker.)
And subreddits are different. I really don't see much connection between Instagram and /r/polandball
Instagram itself is not the problem. How teenagers are using social media is a behavior or perspective issue in my opinion, not a problem with an actual product that just offers a nice tool. Growing up before the internet, these attitudes were in effect, just exposed differently. Honestly I think it is a cultural problem, because there are other places in the world where this obsession with acceptance does not exist, and where everything is not driven by ego or lack thereof.
I'm pretty sure that these behaviors just come from being a teenager and aren't caused by any specific technology.
It's become the mosquito of the Internet, possibly useful in some mysterious way but if I had to choose a species to exterminate it'd probably be that one.