[ethics_gradient]

Well, there is evidence to the contrary, at least: the lack of success of the NSA mass spying programmes, with experts like Schneier repeatedly showing why such programmes cannot in the near future even be useful for their stated purpose (anti-terrorism), and officials from the government admitting that they didn't really get much out of it - just some taxi driver who could hardly be called a threat.

The evidence that such systems endanger safety, meanwhile, should be obvious to anyone who has read about how surveillance has been used, from totalitarian states to even liberal democracies (even in the somewhat recent US history), as well as knowledge of how quickly the latter could turn into the former.