Less relevant to European regulation, but the FBI's attempt to use phone taps/hotel room bugs to blackmail Dr. Martin Luther King, Jr. int committing suicide[0], is a good example of why we should be suspicious of even lawful intercept. Terrorism is bad, but I think we can all agree a world where the US civil rights movement was stillborn would be much worse than what we have. (They went after more civil rights leaders than just Dr. King.) More recently, FISA courts have a terrible record of filtering out unreasonable lawful intercept requests.
Are there any comparable post-WWII Eurpopean abuses that should make citizens think twice about blanket law enforcement back-doors?