"But because a prescription requirement won't hamper Mexican cartels, why stick it to law-abiding Americans?"
Because sticking it to law-abiding Americans is what leftists do. It's all they know how to do, and they wouldn't stop if they could. They're too fastidious to deal effectively with criminals. In many cases they admire criminals or are criminals themselves. And some of the smarter leftists realize that criminals tend to ignore laws. But to feel good about themselves and to win reelection by appearing concerned and active, they have do do something. So they crush the only people who'll take their laws seriously -- the law-abiding.