I do not have to agree with anything you said, to admit that the Slippery Slope should probably be taken off the fallacies list at this point.
the slippery slope fallacy was never stated as an absolute truth; it exists to point out the absurdity in the belief that all things are sliding at all times.
that is to say : the slippery slope fallacy exists to point out that the constant slip isn't a realistic model for every social qualm to have ever existed, and is not universally applicable; not that it doesn't occur.