It's multifaceted, police do sometimes serve as a deterrent to or to protect people, but it's important to also recognize the position they hold isn't to help your average people as much as it is to maintain order for the benefit of the state. They are the internally focused gun that will just as soon shoot a killer as a black child walking down the street with a nerf gun. Either one serves the same purpose, stay in line or else, do what we say or else, they sow fear in the population while making the privileged feel some illusion of safety. They'll help you get your stolen car back, while also arresting a mother for stealing food from Walmart, or a homeless person for sleeping in their car. If you are any sort of minority, a police officer is a much greater threat than a help, and we've seen that in a history of high and low profile cases where police murder black people with absolutely no consequences, or in their use to suppress even the most by-the-book protests. Instead of solving the core problems that cause the majority of crimes, like poverty.