>Suppose the city of San Francisco deported 10 percent of its computer programmers tomorrow and adopted a law saying that in the future no engineers born in other counties were allowed to move here. Would that lead to skyrocketing earnings for the remaining engineers? I seriously doubt it. I think it would destroy the San Francisco tech industry with some unfortunate knock-on effects a bit south in Silicon Valley.

I wonder if there is a name for this fallacy, because I see it all the time. A common example is "Well imagine what would happen to the economy if everyone became a vegan tomorrow!"

As a malicious device for derailing a discussion, it's pretty clever. It pivots the argument from "how would the world be different if Y instead of X?" to "how would the world be different if we instantly tried to switch from X to Y?"

Suppose you propose going to the grocery store. I say, no that's a terrible idea. Imagine if, in the next second, you were suddenly whisked away to the grocery store — the acceleration forces would liquify you! Obviously that would be a dumb thing to say, but you still see these "what if X overnight‽" arguments all over the place.