What is the slippery slope fallacy?

Logical fallacy is making invalid conclusions, or, simply put, a flawed argument.

One of such fallacies is a "slippery slope" fallacy, which basically means, making a claim about an event that will start a streak of events ending in, most often, an awful outcome.

In reality, there is no proof, logical connection or reason to believe that this chain of events will really happen, but by assuming so, the person making the fallacy, is giving the counterargument for the original action.

Basically, if A happens, then B will happen. If B happens then C will happen. If C happens then D will happen. D is an awful outcome. So, if we don't want D to happen, then A shouldn't too.

The fallacy in this reasoning is that B isn't necessarily consequence of A, C isn't necessarily consequence of B etc. So claiming that chain of events occurring is logically invalid.