Even many dictatorship states, like many of the "socialist" countries, had in the past articles in their constitutions that guaranteed the secrecy of the mail and of the telephone communications (other telecommunications did not exist at that time). Thus it is false that there is some kind of established tradition that governments may have access to private communications.

In reality the secret police did not care about laws or constitution, so private mail correspondence was intercepted and opened, read, then closed again with care, trying to make this undetectable, and the telephone lines of persons of interest were tapped.

Nonetheless, it was understood that this surveillance is actually illegal, so it was hidden as much as possible.

Nowadays, the government institutions of most "free" states, like USA and UK have granted themselves far more rights to do surveillance of their citizens than the dictators of the past.

Detecting and prosecuting serious crime does not need any such general surveillance. The general surveillance just makes much cheaper the detecting of serious crimes, but in exchange it gives the means to the government employees to commit more serious crimes themselves.