The point is that a police uniform gives a veneer of respectability to robbery (they even call it something different--a bribe!) that a mugging does not posses, and presents as a routine matter instead of an assault or threat of violence (the threats there, of course, just less explicit). The uniform is a bone-stock, fundamental element of the police bribe dynamic. You can hard disagree that tourists find it more agreeable, but you need to throw out some kind of argument for why that is (more than just how hard ya are).