I should be surprised by it but the police is really nothing special in the US. It's just part of the bigger US theme of giving unvetted people power they do not deserve to wield. Of course people are gonna get hurt if power lies only with sociopaths. And they easily stay in power because people don't know how to utilize and bundle their power to combat it.
If you demand respect or gratitude for your volunteer work, you're doing volunteering wrong.