You're still missing it. The police's job is to enforce the laws passed by Congress or local governments. Those laws in theory are to protect the public or their interests. In reality, there are often bribes (eg big pharma or oil), politics (gay marriage), or just evil (slavery). Enforcing these laws harms the many for the selfish gain/purposes of a few. They'll enforce them anyway.

Later on, someone tries go push against that leaning on the theory that they're responsible for our safety. Supreme Court gets extra clear that they're not. That's while they continue to let laws from bribes stand. Little room for debate now. Also, anyone pushed into confessions using cops and prosecutor's legal right to lie about the evidence already knows system isnt about protecting people. That shit wouldnt exist if it was.

So no, they're neither intended to nor required to "serve and protect." They're instead enforcers of arbitrary laws that can protect or harm individual citizens. From there, individual departments or prosecutors might have policies (as some do) to treat community with respect while focusing activities on reducing actual harms. However, that's entirely voluntary.