There’s an established precedent in (American) law that it’s generally okay to forbid an action but it’s not okay to mandate an action. For example, you can stop people from driving without a license, but you can’t make everyone get a license.

I hate to point it out, but ObamaCare is an example of the reverse: you're mandated to purchase health insurance, or else pay a hefty penalty fee.

Yeah, and that’s part of why it was so controversial. On top of that, op seemed to be suggesting making it illegal - as in go to jail - not having a penalty, which is substantially different.