On the Slippery Slope

Slippery slope, as most people with any passing interest in logic generally know, is a logical fallacy.  It typically takes the form of a claim something like this:

Me:  "Oo, I think I'm going to have some chocolate.  It looks yummy!"
Someone else:  "Are you crazy?!  Chocolate makes you fat.  If you chocolate, you're going to get fatter and fatter until you die!"

What's wrong with this, and what makes it a logical fallacy, is that having a few chocolates doesn't require the consumption of yet more chocolates.  There's no magical force behind eating a chocolate that is going to possess my body and make me continue eating chocolate until I die.  Philosophically, this would be referred to as "necessity".  Chocolates don't necessitate more chocolates, so the argument is invalid.

This seems simple enough, no?  So why do people keep using "slippery slope" arguments?  You see them everywhere.  "If you let people get away with small transgressions, they're going to start making larger transgressions."  "If you inflate the currency, the spending is going to run away."  It's a logical fallacy, so why do people think that this sort of warning has any validity?

It's because there is a correct context in which the form of the "slippery slope" argument (that X leads to more X) is a valid one.  It never becomes logical in the sense that X necessitates more X.  It remains true that if people do X, they can still turn away from X at any time.  This is, in fact, the fundamental axiom of volition.  So how can this argument ever be valid?

It's valid, precisely because people have free will, that is, their minds don't operate automatically.  They can make choices.  This means that people need guidance on how to make choices, so that those choices actually lead them to what they want.  They need to adopt some method of operation, if they want that operation to take them anywhere.  The name for that method is principles.  Everyone adopts some principles, even if they insist that they don't and just do "whatever they feel like".  Doing "whatever you feel like" doing IS a principle, albeit an ultimately self-destructive one.  That's a side issue, for now, though. The important point is that in human thought, some principle or set of principles is always involved.

To adopt a principle doesn't just mean to sit there and dwell on it.  They are guides to accomplishing a goal.  To adopt a principle means to act on it.  And not just once, but all the time.  Consistently.  If I don't act consistently on any principle, I can't be said to have that principle at all.  It's not the same thing as being perfect--people can and do fail to carry out their principles, but on balance, they would have to act on it far more often than not in order for anyone to say that they adopt a given principle.

A principle, once adopted by a person, leads them in a consistent direction.  Their actions, taken under that principle, are pointed at a specific goal.  The more consistent they are, the more direct their course to that goal.  This is where you can begin to see the connection with the concept of a "slippery slope", of X leading to more X.  It's not that they've lost their volition somehow, it's that they've lined up their faculties behind this principle because they are using it to lead them to their chosen goal.  So, if they're doing X because their principle is to do X, you can safely predict that more X is definitely in the future.  In the absence of a change of principle, more X is on the way.

So, if you see a person or group adopting a principle to do X, you CAN make rational assertions about what is on the way.  And shouting "that's a slippery slope argument!" doesn't negate the truth of these statements in any way unless you can provide evidence of either a change in principle or how that principle doesn't lead in that direction after all.