Supporters of surveillance systems believe that these tools can help protect society from terrorists and criminals. They argue that surveillance can reduce crime by three means: by deterrence, by observation, and by reconstruction. It can deter by increasing the chance of being caught, and by revealing the modus operandi. This requires a minimal level of invasiveness.
Another method on how it can be used to fight criminal activity is by linking the information stream obtained from them to a recognition system (for instance, a camera system that has its feed run through a facial recognition system). This can for instance auto-recognize fugitives and direct police to their location.
A distinction here has to be made however on the type of surveillance employed. Some people that say support video surveillance in city streets may not support indiscriminate telephone taps and vice versa. Besides the types, the way in how this is done also matters a lot; i.e. indiscriminate telephone taps are supported by much fewer people than say telephone taps only done to people suspected of engaging in illegal activities.
Surveillance can also be used to give human operatives a tactical advantage through improved situational awareness, or through the use of automated processes, i.e. video analytics. Surveillance can help reconstruct an incident and prove guilt through the availability of footage for forensics experts. Surveillance can also influence subjective security if surveillance resources are visible or if the consequences of surveillance can be felt.
Some of the systems (such as the camera system that has its feed run through a facial recognition system mentioned above) can also have other uses besides countering criminal activity. For instance, it can help on retrieving runaway children, abducted or missing adults & mentally disabled people.
Other supporters simply believe that there is nothing that can be done about the loss of privacy, and that people must become accustomed to having no privacy. As Sun Microsystems CEO Scott McNealy said: “You have zero privacy anyway. Get over it.”
Another common argument is: “If you aren’t doing something wrong then you don’t have anything to fear.” Which follows that if one is engaging in unlawful activities, in which case they do not have a legitimate justification for their privacy. However, if they are following the law then it would not affect them.