There will always be some criminals who are sophisticated enough to evade surveillance (until they make a mistake) - but that doesn't mean it's useless as many

There will always be some criminals who are sophisticated enough to evade surveillance (until they make a mistake) - but that doesn't mean it's useless as many violent and/or organised criminals do get caught. Many get caught even with old-fashioned phone taps. Also, aren't there ways of implementing targeted surveillance without weakening privacy/security very much, if at all? For example, targeting a specific user/device and making sure all exfiltrated data is encrypted with a public key belonging to the police.