Slippery slope arguments are a form of reasoning that links one way of thinking to an unintended consequence that’s likely to follow. With moral issues, if a behavior seems justified but “slips down the slope” in some way to something more drastic, it calls into question the morality of the initial behavior.
Some such appeals are faulty, of course, but some are valid. I want you to know the difference since you’ll likely encounter them. If you claim, for example, that doctor-assisted suicide will lead to involuntary euthanasia or that abortion liberty will lead to infanticide, you’ll likely be dismissed with, “That’s just the old slippery slope fallacy.”
Slippery slope concerns, however, are legitimate factors when thinking through the consequences of moral practices. There are fallacies of this sort, of course, since some acceptable practices don’t lead to extremes. Some do, though, simply by the force of the moral equation built into the issue. Those are the ones to be concerned about.
There are actually two distinct kinds of slippery slope appeals: a causal slippery slope and a logical slippery slope. The nature of each often becomes obvious after looking closely at the underlying circumstances related to the actions in question.
With a causal slippery slope, if some action thought to be morally acceptable leads to a result that’s morally questionable, it casts a shadow on the initial action. Simply put, if some consequence B is wrong, and permitting A will cause B to occur, then A is wrong, too.
Driving fast isn’t intrinsically immoral, but because it’s dangerous and leads to human harm, the wrong of the effect “slips over” into the cause, making it wrong, too. Some think pornography is acceptable, yet if it can be shown to cause violence against women, then pornography becomes morally suspect for that reason.
Unfortunately, many people find doctor-assisted suicide defensible. They often don’t realize, though, that the practice has unintended consequences. Euthanasia starts out as voluntary, then becomes non-voluntary—patients in a coma are euthanized—then becomes involuntary when older, ailing patients are killed against their will. This actually happens in countries like Holland that have liberal doctor-assisted suicide laws.
What needs to be shown to avoid a causal slippery slope fallacy is a clear causal relationship between what some consider morally acceptable actions and the consequences that are morally suspect.
Logical slippery slopes work in a similar way, with one important difference. The relationship between the idea in question and the behavior that follows is logical, not causal. When the rationale justifying one behavior is applied consistently to another behavior, the acceptability of the one “slips over” to the other. So, if A is accepted as morally justified, and action B is logically similar to A, then B will probably be accepted, too.
For example, many abortion advocates consider late-term abortion and even partial-birth abortion (PBA) acceptable according to the logic of privacy and personal autonomy (“choice”). In each case, though, the baby is completely developed, and in PBA, the baby is almost completely delivered.
If these abortions are justified on the basis of choice, then by that logic what objection can be raised against infanticide since the baby’s location is a trivial element in the moral equation? The logic that justifies the first seems to equally justify the second.
A logical slippery slope can slip in either direction, by the way. If one act is morally unacceptable—infanticide—and another act is logically similar to it in a morally relevant way—abortion—then the second becomes morally unacceptable, too.
Here’s an example of a logical slippery slope that fails. Some think capital punishment is logically similar to murder since both involve killing a human being. Consequently, capital punishment is immoral, too.
You probably caught the problem. Since there are morally relevant distinctions between murder and capital punishment—namely, the guilt of the one punished vs. the innocence of the one murdered—the attempt falters. This appeal, then, is an example of a slippery slope fallacy.
The key question in any logical slippery slope claim is whether the two situations are similar in a logically relevant way. If the analogy fails, then the attempt is fallacious and the argument falls apart.
Here’s the lesson. Don’t let critics flippantly dismiss slippery slope concerns that you raise regarding moral issues. Both causal and logical slippery slope considerations are legitimate when constructed properly, and both play a critical role in providing clarity on weighty moral issues.