I see the full meaning of ACAB as: if you participate in a system widely regarded as championing bastard-like behaviour then you yourself are a bastard by proxy and/or association.

Some cops actively try to change the pervasive bastardishness, they are not cops for very long , the latest example.

Some cops are there because they need to feed their kids(or themselves), still bastards, but with a relatable reason (perhaps even approaching a viable excuse) as to why they continue to make that choice.

if your argument is that at any point in time, there is the possibility of a non-bastard cop existing because they haven't been murdered, exiled, scapegoated, indoctrinated. converted or quit yet....then yes that is technically correct.

This, like everything else, is subjective.

If you are rich and/or powerful enough to be considered inside the demographic the police were designed to actually protect (as opposed to control) then i'm sure it's a much less bastardlike experience.