Actually, in most cases having fewer police on the streets leads to LESS petty crime.

This is because cops tend to spook people, so everyone (including the innocent, law abiding citizens) will leave areas that are patrolled.

This creates the ideal scenario for crime: there are few/no witnesses around for a while after the cops come by.

In pretty much every case I am aware of where cops go on strike and stop doing regular beat patrols, crime goes DOWN.