[harimau777]

It is a fallacy to say that the slippery slope will always occur. However, that does not mean that it is invalid to argue that in a given situation a slippery slope is likely to occur. In cases such as this I think we can reasonably assume that the "never" in "it never stops where you think it should" is not meant to be taken literally but is instead being used as a figure of speech for "very unlikely".