At the root of all this is an issue of privacy. A fundamental question would be: do you/we have a right to privacy. My opinion is no.
We do have a right to be secure in our persons and property against illegal search.
Are bits you've shared on the public internet still your property? (I think no) It's information you're sharing with the public and/or giving to a third party (Google, Facebook, Twitter, &c)
Many (most?) of these sites operate with a TOS that gives them some ownership/control of the data. If you give your data to Facebook and they give it to the Gov have you been illegally searched? (I think no)
Has FB been illegally searched? (I think no) However heavy-handed some of our recent-ish terrorism laws may or may not have been it would have been resting on these third party providers to fight since it appears they are the only one who have a claim on illegal search.
My fundamental belief that we have no *right* to privacy - it's one of the reasons I make&sell encrypted communication tools.