The EFF has published a well-cited and informed article on why they view the current trend of dragnet surveillance to be thoroughly against the constitution of the U.S.
Even if you are not an American, this article touches on the ideals of many. It describes the context around why the Fourth Amendment was included and goes into specific detail as to who and why they thought it so important:
“Using ‘writs of assistance,’ the King authorized his agents to carry out wide ranging searches to anyone, anywhere, and anytime regardless of whether they were suspected of a crime. These ‘hated writs’ spurred colonists toward revolution and directly motivated James Madison’s crafting of the Fourth Amendment.”
I highly recommend reading the entire article: The NSA’s “General Warrants”: How the Founding Fathers Fought an 18th Century Version of the President’s Illegal Domestic Spying