Given that police officers

(a) are first-responders whose central job is public safety,

(b) are regularly sent into situations where their life and safety is on the line (6 have been shot to death in the past two months), and

(c) regularly face violent and hateful prejudice as an identity, just for putting on the uniform,

it's hard to justify that they don't deserve advocacy from a group of people with shared experiences.

It doesn't mean that unions should always get their way or that unions should be officially recognized, but police can and should exercise their rights to collectively bargain and strike if necessary.