Final answer:
Mobley's main idea is that laws cannot effectively control people's moral behaviors, as seen by the failure of prohibition laws.
Step-by-step explanation:
The main idea of Mobley's argument is that laws that are written to control people's moral behaviors cannot be effective. Mobley argues that laws attempting to legislate morality and impose religious views about alcohol are rejected by many Americans and inspire disregard for the laws. The failure of prohibition laws to prevent the manufacture and consumption of alcohol, as well as the increase in bootleggers and speakeasies, supports Mobley's argument.