A popular flawed argument among fearmongers. It’s an argument of connected occurrences of events leading to a disastrous end state.
The schematic view of the slippery slope fallacy is as follows.
1. If A, then B
2. If B, then C
3. If C, then D
4. not-D
Therefore, non-A
Let’s substitute for the steps using a simple example.
If you miss this homework (A), you will fail (B)
If you fail (B), you miss getting admission to college (C)
If you don’t attend a good college (C), you will not get a job (D)
If you do not have a job (D), you will be poor and homeless (E)
Therefore, you must do the homework.
The proponents of the slippery slope fallacy assign certainty for each step. They consider the impact like a domino, where the fall of one guarantees the collapse of the next. This is far from true in real-life situations where there are probabilities. In the above example, even if the chance for each event to happen is high, say 80%, the overall probability of becoming homeless is less than 50% (0.84).
A notorious example from history for this domino theory is the US involvement in the Vietnam War. The argument of President Eisenhower in 1954 was that if Vietnam were allowed to become a communist state, the neighbouring countries and neighbouring regions would become communists, leading to “incalculable consequences to the free world.”
Reference
The Small Sample Fallacy: Kevin deLaplante