[zby]

This is a good argument - but I don't entirely buy it - because a system like that does not need to lead the investigations, but can also be an additional source of information. A very powerful one - if the police is already investigating someone than the possibility to browse all his history, his contacts etc. would be very useful.

[barrkel]

That's even worse - "Give me six lines written by the most honest man in the world, and I will find enough in them to hang him" - if you're looking for guilty-seeming people, you'll find them.

And if you're trying to prevent atrocities, you'll convict them before they've done anything wrong.