I think it's because FB is basically a modern day white pages, whose core mission is mine user data and deliver ads to people who don't want to see them. I think much of the disdain is in the fact that a company like this can manage to gain so much valuation in the first place.
Not saying I necessarily agree with that, but I can at least understand how it does leave one with the impression that priorities in the tech industry and wall street are completely out of whack. Instead of solving 'real' problems (energy, medicine, education, etc.) we disproportionately value some rather inane activities.