Argument from Consequences

An Argument from Consequences or argumentum ad consequentiam (Latin for "argument to the consequence"), is a logical fallacy where the truth value of a statement is called into question by appealing to the consequences it would have if true (or false).

The fact that a proposition may lead to some unfavorable outcome would not render it false, and vice-versa. This means that this is only a fallacious argument when it is used to support of deny the truth value of a statement, not when discussing consequences or decisions.

This concept is closely related to appeal to emotions or wishful thinking.

Forms
An argument from consequences generally takes on one of two forms, positive or negative:

Positive Form
If P, then Q will happen. Q is a desirable outcome. Therefore, P is true.

Examples:
 * I believe in an afterlife, because I want to exist forever.
 * Humans must be able to travel faster than light, because that will be necessary for interstellar space travel.

Negative Form
If P, then Q will happen. Q is an undesirable outcome. Therefore, P is false.

Examples:
 * God must exist; if He did not, then people would have no reason to be good and life would have no meaning.
 * Evolution must be false: if it were true then human beings would be no better than animals.