Rarely is a popular slippery slope argument (whether an accurate prediction or not) an actual logical fallacy: Most of the time when people accuse something of "The Slippery Slope Fallacy", they're mistaken as to what an actual logical fallacy actually is.

A legitimate logical fallacy of the "slippery slope" variety is when one observes a transition from state S_0 to state S_1 via some step/action X taken, and without evidence or justification (!) assumes/claims that the step/action X will therefore be repeated indefinitely until the system evolves to state S_2, S_3, S_4, ... S_n (where S_n is presumably a state we all consider to be undesirable). The "without evidence or justification" part here is EXTREMELY important. If you actually have evidence or justification of a slippery slope, it is not a fallacy; it becomes a valid argument.

Tip: When you see what looks like a slippery slope fallacy at first glance, it's probably best to give the opposing argument the benefit of the doubt by asking for evidence/justification for the induction (S_0 -> S_1) -> S_N. In most cases, some evidence will be provided to justify. If you disagree with the justification, the debate continues in that direction (which is good, because this is productive).