Hidden Slippery Slope Risk and the Ad Hominem Heuristic

[This month, I’m serializing my 2003 Harvard Law Review article, The Mechanisms of the Slippery Slope.]

The discussion above has assumed that we know up front the preferences people have among positions 0, A, and B. But sometimes B might not even be considered at first, and the apparent choice might just be between 0 and A: for instance, returning to the enforcement need slippery slope example, shall marijuana be legal (0) or be subject to mild penalties (A)? Instead of the complicated mix of preferences I described in that post, we might at first see just two large groupings: a minority opposing the mild prohibition, and the majority supporting it. The risk that the mild law won’t be complied with, which might lead to sterner measures, might not be much discussed.

Then, once the mild prohibition A proves ineffective, the hard-core war-on-drugs plan B will be brought up, and may succeed politically (if the preferences are as described in my earlier post). Some supporters of the mild penalty plan would regret their actions: they would rather stay with A, or even go back to 0, because they strongly oppose B; but their endorsement of A back when B wasn’t even discussed now makes B possible. They might wish that they had thought earlier about the enforcement need slippery slope—but it would be too late, because there would now be a majority for going all the way to the newly proposed B.

This slippage is especially likely if A fails not just unexpectedly, but also because of changed circumstances. Say the United States is deciding whether to commit troops to a small peacekeeping mission in a foreign country (A). When this decision is being made, committing more troops to a broader military action (B) may not even be contemplated. But if the modest disorder that prompted the mission turns into a full-scale war, option A would no longer be feasible; we’d have a multi-peaked slippery slope, and A might slip to B even though B wouldn’t have been authorized up front, without the initial step A.

And slippery slope risks might also be hidden—especially f