What the Fallacy?!
Slippery Slope
The Fallacy
Asserting that if we allow A to happen, then Z will eventually happen too, therefore A should not happen.
Why it's wrong
The problem with this reasoning is that it avoids engaging with the issue at hand, and instead shifts attention to extreme hypotheticals. Because no proof is presented to show that such extreme hypotheticals will in fact occur, this fallacy has the form of an appeal to emotion fallacy by leveraging fear.
Example
If we allow students to have five extra minutes for lunch, next they'll want an hour, then they'll stop coming to class altogether, and eventually the entire education system will collapse into anarchy.