Slippery Slope is not necessarily a fallacy because it's a very real phenomenon. My test is examining the "slippery slope" by asking if it instead "establishes a precedent". And then I see how easy it might be to justify going further down such a path based on past justifications.

Fair, I just don't see how my acquiescence to one thing is an endorsement of a distinct, if similar, thing.

I guess I reject the idea that policy (a well considered and debated, long lasting decision) would actually fall for something like a slippery slope.

The proverbial boiled frog just jumps out of the pot when the water gets too hot, in reality.

I appreciate that, and for what it's worth I agree you that slippery slope/establishing a precedent is countered with concrete and well thought out criteria that need to be met.

That the slippery slope is an inevitability is the fallacy, not that it exists. See also "Overton window"

No, because of group dynamics. Once you start un-personing people, you have the in group and the out group. The in-group repeatedly redefines acceptable behavior to exclude some small margin. Repeat and you end up with absurd extremes.