To me, Instagram is the culmination of photography, making shooting and editing available to truly everyone. When photography first appeared, it was this slow, clunky, expensive process that required extreme knowledge of the tools to produce anything. Over time, it got easier - we went from daguerreotypes to self-contained camera, to portable cameras that still required fiddling with settings, to portable cameras that could take shots in almost any conditions, to instant cameras, to digital cameras that still require effort to share the picture, to digital cameras that can share the picture instantly to the entire world.
And in counterpart to that, the editing process has gotten simpler too: we went from needing to know the chemicals of photography, to bringing your film at your local store, to tools like Photoshop (that allowed you to crop, adjust colors etc. but still required knowledge to do so), to Instagram: where there's no manual to read, and an instant a 12 year old teenager or a 75 year old grandparent can crop, retouch, color balance, etc. their photos.
Sure, the purist might argue that Instagram filters are not the same as balancing your chemicals yourself, blablabla - but look at the end result: people are able to take ownership of photography in ways that were impossible to in 1840. Ultimately, photography, like any form of expression, is as much about the tools that enable it as the people it reaches.
Because Instagram (and other mobile photography apps of course, but Instagram is kind of the figure head) have put photography in the hands of everyone, I think they've really brought the medium to its best form.
(my views on this topic are mostly informed by the book "L'Image Sans Qualités", sadly only available in French, and conversations with my uncle, a hardcore photographer who develops his own pictures and builds (!) his own cameras from scratch, also sadly only available in French)