Absolutely using Facebook and Google is a declaration of that. At least the government is incompetent, by sending that information to Google and Facebook you're leaving yourself up to their good graces (which change with little to no notice which each modification to their privacy policies). That is a person's own choice to make, but they've definitely made it.

The 4th Amendment covers the relationship between you and the government. It does not cover the relationship between the government and a third-party, unless Congress passes additional legislation to add that protection.

Congress has done so for the mail, for landline telephone, beepers, and cellular telephones. They have not done so in the general case for email or other electronic data hosted by a third-party, and yet email and other electronic services somehow have become incredibly popular.