"[..] it's fair to say that the majority of law-abiding citizens would want prosecutors to be able to access evidence that could help convict someone of a serious crime, regardless of how strongly they feel about their own personal privacy."
That is a very large assumption - I'm sure there is a legal expression for using such a tactic to try to sway an audience.
The public are getting wise to the agencies crying wolf - and then using their new powers to go after law-abiding citizens for what might not even constitute minor offences. They are easy targets to boost the agencies' statistics.
An underlying principle of English law is that it is better for nine offenders to go free - than one innocent person be unjustly convicted. We live with the risk - and that is an essence of democracy. No one would wish to live in a world where law-abiding citizens were automatically regarded as guilty unless they could prove their innocence.
The Edward I "hue and cry" was very unpopular with the general populace. It often meant a community being forced to hunt down one of their own for a "crime" against the unequal power of the elite. The punishment for failing to take part in the "hue and cry" was draconian. Citing some governments who have done that would invoke Godwin's Law.
Biting the hand that feeds IT
