Attention is a zero sum resource, and humans can be manipulated into spending their time in ways that are not in their best interest.
Edit: Tristan Harris has written interestingly on this topic:
http://www.tristanharris.com/2016/05/how-technology-hijacks-...
What if it teaches users the habit of selling crack cocaine? (stupid example, but you get the point)
In that vein of thought, maybe OP had a point. Snapchat/Instagram seems to feed our narcissistic egos more than anything, so maybe it's not as morally inert as I had thought.
PS: Despite being recorded "with a potato", to borrow the first comment, very relevant to basically all social media and moral good. And Bo Burnham is an amazing watch generally anyways, PSA. All of his specials are gold.
I would argue one is morally acceptable (building the app) and the other isn't (selling crack-cocaine).