As long as you cooperate with the police they usually will be nice and treat you with respect most of the time! Try telling one you believe he/she is wrong, immediately his ego become involved. Not wanting to be wrong and protecting the ego he/her do whatever it takes to prove that he's right even if that means hurting someone!
Is that an abuse of power? Most people act this way in their everyday lives, just go tell anyone you think they are wrong, and see what happens!
The only difference is the police have the ability to hurt people whether it be financially, physically or with the court systems without consequences. The police need someone to answer to, all their actions should be judged and scrutinized. But being a police officers is a really hard job and the honest ones out there risking their lives every day, to keep us safe!