It’s happened to all of us at one time or another.  You’re having an argument, calmly and coolly explaining to someone that although a particular policy might not have any immediate negative effects, you still oppose it because you believe that down the road, it will lead to negative consequences in the future.  Before you know it, you’ve been beaten.  Your opponent starts screaming “SLIPPERY SLOPE!” and declares the argument over, with himself the victor.

What a bunch of nonsense.  The infamous “slippery slope” is absolutely NOT a logical fallacy.  Rather, it is a simple attempt to acknowledge the obvious:  that occasionally, certain actions have consequences that might be long-term in nature and that might not be immediately obvious to the casual observer.  To declare that the slippery slope is a logical fallacy that can be dismissed in all cases is essentially to argue that every event in the universe is independent.  That any particular action cannot possibly lead to another particular action, and that any implication it might is automatically to be dismissed as proof that the person implying such is an idiot, not to be taken seriously.

In the political realm, the slippery slope accusation is most often invoked against those who oppose a certain change in policy.  Let’s say that Policy X is currently being debated.  Those in favor of Policy X believe that it will confer benefits onto the nation as a whole, both immediately, and into the foreseeable future.  Meanwhile, the opponents of Policy X cannot readily identify any immediate harm that may come as a result to it.  Their opposition relies solely on the fact that they believe Policy X will lead to negative consequences several decades from now.  Obviously the appropriate thing to do would be to evaluate the claims made by both sides.  Are these negative future consequences likely?  If they did happen, how severe would they be?  To the extent that the argument can be settled, it should be settled by an evaluation of the likelihood and severity of the potential positive benefits or negative consequences suggested by either side.

Unfortunately, in modern political discourse, this sort of evaluation is incredibly unlikely.  It is far more likely that the proponents of Policy X will simply declare that the opponents are making a slippery slope argument, and that therefore their entire argument can be discarded as a fallacy.  Sadly enough, most people seem to accept this as perfectly legitimate reasoning.  It is not.  The fact that human beings are capable of anticipating future events proves that a slippery slope argument can be perfectly valid.  To automatically dismiss any “X could lead to Y” argument as fallacious is to essentially resign yourself to a deterministic world where no actions we take can possibly affect future events.  Where nothing we do ultimately matters anyway.  I consider that to be unbelievably depressing, and that’s not the sort of world I choose to live in.