Firstly we're not talking about "terrorists" but people who intelligence services have "received a signal" about. That's pretty ambiguous but sounds like it cou

Firstly we're not talking about "terrorists" but people who intelligence services have "received a signal" about. That's pretty ambiguous but sounds like it could mean an anonymous tip-off or information from another department. Secondly, no one's suggesting that they let everyone go their merry way without looking into anything. Only that widespread surveillance must be justified e.g. the evidence must pass some threshold and other responses have been ruled out.