Appeal to Consequences

This one is more or less two fallacies in one, because it is used both in the positive and negative.

Appeal to Consequences
Other name(s): Appeal to Consequences of a Belief, Argumentum ad Consequentiam (argument to the consequences), Argumentum ab Inconvenienti (argument from inconvenience)
Type: Informal
Category: Red Herring (Irrelevance)

Definition
Arguing from the idea that belief in a proposition leads to good consequences, and therefore the proposition is true, or that disbelief in a proposition leads to bad consequences, and therefore the proposition is false.

Usual Form
Because belief in A leads to desirable outcome B, A is true; because disbelief in A leads to undesirable outcome C, A is true.

Explanation
Appeal to consequences often receives the amendment "of a belief" to its title because it is most often used on an otherwise unproven belief. The idea is to prove that the premise is either either true or false based on whether the premise leads to desirable or undesirable consequences. It is a fairly transparent appeal to emotion as logic, and adds subjectivity to what should be an objective appeal.

As stated on fallacyfiles.org, "one can tell that the fallacy is being committed because the supposed consequences do not follow from the proposition itself, but only from belief in it."

Now, appeals to consequence have certain valid (non-fallacious) use when they refer only to the truth or falsity of an argument's logical consequences. Because understanding the difference between logical consequences and causal consequences is, to be honest, less common than I would prefer, one is often switched for the other. A second situation which can be confused for an appeal to consequence is consideration of the results of a plan or policy. Looking ahead to the outcome or repercussions of one's actions is not only logical, but foolish not to do. Likewise, "argumentum ab inconvenienti" is a valid appeal to consequences found in law, in which an otherwise reasonable law or action is shown to have unreasonably inconvenient consequences. People who warn about the "law of unintended consequences" regarding political doings are invoking this concept.

It is interesting how often this argument is used in historical dramas to demonstrate the primitive thinking of law in earlier times.

Examples
"I know that Santa Claus exists because just knowing he was coming each year made me behave better every fall and winter."

"If the six men win, it will mean that the police are guilty of perjury, that they are guilty of violence and threats, that the confessions were invented and improperly admitted in evidence and the convictions were erroneous... This is such an appalling vista that every sensible person in the land would say that it cannot be right that these actions should go any further." Lord Denning in his judgment on the Birmingham Six.

"There is no God, because no righteous creator could allow evil to exist."

"It can never happen to me. If I believed it could, I could never sleep soundly at night."