To say that ANY slippery slope argument is automatically wrong is to say that every single event is entirely independent of every other event. That nothing ever leads to anything else.
To my understanding slippery slope is misrepresenting the opponent's stance by exaggerating it to make it seem ridiculous. Case in point: LordoftheMorons said we should prevent unwanted pregnancies because it's beneficial to society. You replied: "well, surely you must also think killing old people is a great thing to do, because that'd also be beneficial to society!" This is a ridiculous argument.