Exactly, cops can impose force on you and their jobs requires them to do it. If they wouldn't have body cams, it would be hard to see if coercion was justified or not. Surveilling powerless folks works in the other direction. It only serves to make them easier to discipline and teaches them that deviations from approved behaviour will be deterministically punished. And I also don't believe anyone is currently paid to act on their best behaviour as a simple citizen. Although this kind of monitoring works quite well for children under 6, you don't want paternalistic institutions, since you will never outgrow them.