The underlying assumption for funding is that the police gets money from the city, and if you reduce that the police will have less money - and for some reason they would then do less of the bad stuff.
Most people would say 'no shit, sherlock' for the first part; but in reality it's not that simple.
The reason is that the police have found other sources of income. Ferguson PD to name a bad apply, did rely a lot on fines and fees (traffic violations, badly cut grass, etc), and others have relied on civil forfeitures. Reducing funding without any other changes may cause the police to rely even more on those "alternative sources on income" - which both counters the funding change and is bad in itself, and rely even more on military surplus (free of charge).
To inform yourself:
FERGUSON LAW ENFORCEMENT EFFORTS ARE FOCUSED ON GENERATING REVENUE
https://www.justice.gov/sites/defaul...ngs_3-4-15.pdf
Ferguson may have improved since then, but I'm sure other police departments would do the same if they could get away with it - especially if they felt they needed the money.
That lack of analysis is what happens when you don't try to pragmatically solve the problem, but go for LARP-slogans.