As an armchair economist who believes that everything DOES happen at the margins, we can't completely ignore this, so I'm at least somewhat sympathetic to the argument.
But what really kills the argument is looking at how our medical professionals have stepped up and responded to COVID-19, putting their lives on the line every day, with utterly inadequate gear. And still they serve.
Yes, if the police are less militarized and have more personal liability/responsibility, it will reduce the level of interest in the profession somewhat, but I think we have to not kid ourselves about the degree of such an impact.
This is before we get into whether we really even want "those people" (who are attracted to the militaristic side of policing) 'serving' our communities at all.
Just as anti-pursuit policies have swept the nation to reduce officer-involved carnage, we can reduce escalation of violence.
It seems obvious to me that as we work toward decarceration and decriminalization there will be a need for fewer police officers.
Practically everyone agrees that racial profiling should go away. Well, that's less "work" and should lead to fewer staff. Pretty similar public sentiment toward drug possession.
Not quite cops, but related. If we got rid of cash bail we'd need smaller prisons and fewer corrections officers. People who are released without bail overwhelmingly return for their court dates. So the only reason they are in jail is because they couldn't afford bail--they haven't been convicted of a crime. And that bail is then used to coerce confessions out of people.
On a given night, about 470k people are in jail because they couldn't make bail. That's about 25% of incarcerated people.