From the point of view of comparative economics, "defund the police" is not that hard to understand. Superficial thinkers immediately start worrying about the totally hypothetical other end of the spectrum -"What will we do without the police?"- instead of considering that the current system is an extreme. Nobody said, not even on a handwritten placard held up at a rally to draw attention to the issues with the criminal "justice system", nobody said, "Completely defund the police." Just one example of a completely reasonable question underlying the demand to defund the police is why 75% of the budget for the unhoused goes to policing them.
Quantitatively, how low can we go with "defund the police"? Well, if we insist on being the "topmost nation in policing" in the world, which means having just a bit more cops per capita than the second worst nation in the world, we can reduce policing in the US by 75% and still be "first"! Even with the largest police force in the world, US cops can't stop bikes theft at BART or CalTrain stations, can't solve minor property crimes, can't find lost or misplaced cars, in fact they don't even want to register bike theft. All they are good for is shoot-em up. That isn't law enforcement, that's thuggery!
Where do we go from here? How about to where other nations are, starting with reducing the US police force to a quarter of what it is right now? How about demilitarizing the police? In the words of Commander Adama of Battlestar Galactica, "There is a reason we keep the military and the police separate. The military exists to protect us from enemies of the state. The police exist to serve and protect the nation's residents. When you make the military police the nation, you make its citizens the enemies of the state."
Which explains a lot.