And the winner is…
Hypothesis No. 8: Cubin's sons would not be suspected of being drug addicts, and that's unfair. From reader Eugene Volokh:
" … or does that mean because my sons look like they aren't drug users, they wouldn't be harassed when other people might be? Because that's the problem—I do not believe in stereotyping anyone, any time, ever, for anything, but when you've got a law like this on the books, people will stereotype potential customers based on what they think a drug user looks like."
This entry is not racist, is decently logical, and actually returns to the subject at hand, which is the amendment banning the sale of guns to drug addicts. It's still faulty on the grounds that someone would have to knowingly sell to drug addicts in order to be prosecuted. But Chatterbox likes its elegance.