I would like to contribute the point to back this up that the question isn't really e.g. "is it OK to wiretap murderers?" Actually, it's "is it OK to wiretap suspected murderers?" And the second one is a vastly greater burden. It means we need to trust the guys who decide who to suspect. This is far from a solved problem, of course, as most people agree that some justice system is necessary, and it's a hard line to draw, but the point is, one must be extremely wary of granting broad powers over arbitrary people without requiring an amount of evidence proportionate to the damage exercising those powers will do to them.
In short, if you just say "who cares about suspected murders, probably most of them are murderers", you are leaving a lot of discretion over your life and the life of those in society around you into the hands of those whose power it is to enforce the law. And while they might be the best people for the job, ultimately they are just people too.
In short, if you just say "who cares about suspected murders, probably most of them are murderers", you are leaving a lot of discretion over your life and the life of those in society around you into the hands of those whose power it is to enforce the law. And while they might be the best people for the job, ultimately they are just people too.