Wiretapping was also used by all police states to preserve dictators, by eliminating competition and punishing citizens for wrongthink. As citizens of a country behind the Iron Curtain, my parents were always afraid to talk on the phone, because the secret police was always listening, either directly or via informants.

You're going to say that in democracy, the state uses warrants issued by a judge for wiretapping and there's due process. How's that working out in the US, given Snowden's revelations and the Patriot Act?

Leftists wrongly think that the state represents the will of the people. It doesn't. Democracy is preserved primarily by (1) a culture of liberalism and (2) the state having limited powers. But as could be seen in WW2, democracy is fleeting, actually.

Being from Eastern Europe I've got to say that seeing privileged Westerners willingly give up freedoms, that other people died for, has been such a huge disappointment.

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As for crime prevention and investigation, you can still follow individuals around, install bugs in their home, compromise their personal devices. But it's never enough, is it?