General information on slippery slope arguments

The slippery slope argument is a figure of reasoning by which an action that seems morally acceptable is conclusively shown to be morally impermissible in reaction to its morally unacceptable consequences. In general, two variants of slippery slope arguments can be distinguished based on two possible consequences: the causal variant and the conceptual variant.

The causal variant postulates that the introduction of a practice that is morally acceptable will, with a certain probability, also lead to the establishment of a morally unacceptable practice in the future. Therefore, contrary to first appearances, the morally acceptable practice had better not be introduced. A recurring weakness of causal slippery slope arguments is that in most cases it is difficult or impossible to provide serious and accurate data on probabilities for the occurrence of the undesirable consequence. Even if plausible probabilities can be identified in individual cases, a causal slippery slope argument is only valid if the negative consequence is both sufficiently weighty and if its probability of occurrence is high enough to outweigh the foreseeable benefits associated with the introduction of the morally acceptable practice.

The conceptual variant of the slippery slope argument often occurs in a certain variety, the so-called vagueness variant: If action (1) is permissible, then an action (2) that deviates minimally from it is also permissible, which in turn justifies an action (3) that goes beyond it, and so on. Thus, one finally arrives at an act (n) that is morally unacceptable. But since act (n) is logically related to act (1) via a chain of minimally deviant acts, proponents of this argument conclude that act (1) is already impermissible. Note that conceptual slippery slope arguments may fail because the minimal differences between the acts in question are shown to be ethically relevant: this would reveal that only the introduction of act (1) is justified, but not the introduction of acts (2) to (n). 

Whether or not a slippery slope argument has the theoretical shortcomings outlined must be examined on a case-by-case basis.

Slippery Slope Argument in the case of active euthanasia

A causal variant of a slippery slope argument against active euthanasia regularly occurring in society and moral philosophic literature reads as follows: Legalisation of active euthanasia which remains on an autonomous decision of the person concerned will probably lead in several parts of the population to the development of an attitude of expectation, that seriously ill, suffering humans in certain situations should make use of active euthanasia. Due to such (or also due to a, by those affected merely imagined) attitude of expectation, it would come in several cases to a utilisation of active euthanasia also by those persons, that would actually want to continue living. This would however be morally unacceptable, so that active euthanasia should not be legalised.

This variant of the causal slippery slope argument is indeterminate at its central points: How great are the single probabilities in X-many humans for the development of the according attitude of expectation regarding the utilisation of active euthanasia? How great are the probabilities that, Y-many humans, following the attitude of expectation, would make use of active euthanasia, that would actually want to continue living? Answers to these questions will also heavily depend on the arrangement of the legal regulation of active euthanasia. Risks of abuse could be reduced by considerately established counselling centres and period regulations. But even if satisfactory answers to these empirical questions could be found, it remains a matter of weighing up. Because it is to be noted that a certain number of humans, that commit themselves autonomously to the utilisation of active euthanasia, would benefit from the legalisation of euthanasia. How large may the risk of abuse be, and how large has the number of those persons benefiting from euthanasia to be, so that the legalisation of euthanasia is justified or even imperative?