The words “for public use” are actually in the 5th Amendment, and were included as a clear and hard limit on governments’ powers of imminent domain. Yet five supreme court justices ignored those words.
I don't think the word “privacy” is even in the Constitution at all. Further, I do not think “privacy” can be an issue when discussing things that a person willingly posts to a web-site or web-sites which can, will and are intended to be, viewed by millions of people.