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.
The slippery slope is an informal fallacy. Which is to say, people want a short hand way of dismissing arguments, while also not needing to justify the dismissal, so they conflated actual bad arguments with other heuristics. Just don't tell our secrets to the idiots or conspiracy theorists my fellow big brained skeptic tips his fedora
