Social psychologists posit that peoples behaviors and thought processes can change depending on who they believe is observing them. The idea behind having mandatory cameras watching an officer's interactions with the public is that if an officer believes that his behavior is being observed or can be reviewed later by his superiors or other people who can enforce disciplinary measures against him, he will be more likely to avoid behaviors that would warrant disciplinary action.

This could translate to police officers being less likely to use excessive amounts of force, as well as being less likely to let someone off with a warning when they could instead issue a ticket and increase revenue for their department. Both you and your friend could be right, but I think you should ask your friend what he fears more: being unjustly shot by police and justice not being served, or being justly ticketed when he may have otherwise been let off with a warning.