Right Analogy, Wrong Analogee

Here's an insightful observation from President Bush at a Q&A session he participated in earlier today:

It also makes sense to take pressure off the border by giving people a legal means on a temporary basis to come here, so they don't have to sneak across. Now, some of you all may be old enough to remember the days of Prohibition. I'm not. (Laughter.) But remember, we illegalized whisky, and guess what? People found all kinds of ways to make it, and to run it. NASCAR got started -- positive thing that came out of all that. (Laughter.)

What you're having here is you've created a -- you've made it illegal for people to come here to work that other Americans won't do, and guess has happened? A horrible industry has grown up.

Sound point, sound point. Except, I've got a niggling feeling that this analogy is even more apt for some other public policy question… what could it be, what could it be?