Final answer:
An antidrug policy that decreases the supply of heroin could increase street crime if the demand is highly inelastic as addicts will go to great lengths to obtain the drug, potentially leading to more criminal activities.
Step-by-step explanation:
When considering antidrug policies and their effects on street crime, understanding the elasticity of demand for substances like heroin is important. If the addicts' demand for heroin is highly inelastic, an antidrug policy that reduces the supply of heroin might increase street crime, because addicts are likely to continue seeking the drug despite higher prices or decreased availability, potentially leading to criminal behavior to fund their addiction. This is similar to the case with cigarettes where if the demand is inelastic, increasing taxes leads to higher prices but does not substantially affect the quantity of cigarettes smoked by adults.