Is the slope really that slippery?

I am skeptical about "slippery slope" arguments, whether in theology or politics.

``If we allow/believe X then we will end up with Y, something that is really bad.''

First, this an argument from fear, not from faith and love.
Second, this video makes a point I had not thought of before. Usually, these arguments are against some view/action that is considered "liberal". However, one should be just as concerned about being too "conservative". For example, in theology, trying to avoid liberalism can lead to legalism, division, or authoritarianism.
In politics it can lead to totalitarianism.