I propose the "Line-in-the-Sand Fallacy" as we have seen with liberalism and gay marriage
that the constant invocation of the slipper slope can be a fallacy.

Definition: The Line-in-the-Sand Fallacy occurs when someone arbitrarily declares that a current trend, process, or sequence of events will stop at a certain, self-defined point, as if drawing a "line in the sand," without providing a logical or empirical reason why it cannot be crossed. It mistakes a rhetorical or psychological boundary for a physical or systemic one.

The Core Error: Believing that because you can imagine a stopping point, a natural stopping point therefore exists.

See gay marriage which lead to transing kids.
Female voting destroyed the marriage and birthrates.
Israel and Gaza just because you can imagine them accepting a deal does not mean they will.