The slippery slope argument is only a fallacy when slipping down the slope doesn't actually happen (or can't possibly follow from the described beginning state)

The slippery slope argument is only a fallacy when slipping down the slope doesn't actually happen (or can't possibly follow from the described beginning state). Some slippery slopes do actually exist. For example, if you put your weight over the line, you can literally slip down a slippery slope. On the subject of categories, they cease to be useful when the contents of the categories can no longer tell you anything about the category itself. The further you get down this axis, the less useful the category is. So any dilution of the strength of a category by overly broad inclusion should be scrutinized.