Truth is not dependent upon consequences: Appeal to Consequences

This is the appeal to consequence, and it's a logical fallacy that occurs when someone argues that something cannot be true because the consequences are unacceptable (or is true because the consequences are desirable). This is a fallacy for several reasons: 1) desirability is a subjective concept; 2) it seeks to convince through an emotional appeal as the consequences often evoke fear or desire; and 3) it is teleological in nature (reverses cause in effect) by asserting that something is caused by its own effect. The consequences of something are irrelevant to whether or not it actually exists; children may behave well if they believe in Santa, but that does not mean that Santa must exist. Consequences can be taken into consideration when the argument is whether or not something is desirable, just not whether it is true. In trying to determine a plan of action, it is very reasonable to consider consequences (prescribing drugs, for example). However, that doesn’t mean that something must be false because it doesn’t work out how we want it to. (Other names include argument from consequence, argumentum ad consequentiam, and appeal to consequences of a belief). 

How it applies: This is very common in creationist circles who cite perceived negative consequences of evolution and global warming as the reason that they must be false. Common versions of this include dismissing evolution because it would mean no afterlife, would lead to immorality, would mean that we are related to animals, or to "selfishness, aggressiveness, and fighting between groups" (Henry M. Morris, The Remarkable Birth of Planet Earth). It also includes dismissing global warming because it would result in economic and policy changes, and environmentalism because it suggests some measure of population control. When individuals cite positive consequences for believing God as the reason to believe, they are also committing this fallacy. Common versions of this include moral choices, charity, desiring eternal life, wanting a purpose in life, and Pascal's wager (the consequences of disbelief if God exists is greater than the consequences of belief is God does not exist).

Examples:

• “The universe has all the properties necessary to support life; therefore, it was designed specifically to support life (and therefore had a designer).”
• “Racial integration is bad because we no longer maintain separate bathrooms and water fountains which results in job losses for plumbers."
• “Interracial marriage is bad because people of difference races have different faiths, and someone would have to give up their beliefs to make it work.”
• “Pi is probably a rational number: being rational would make it more elegant."
• "Real estate markets will continue to rise this year: home owners enjoy the capital gains."
• "Humans will travel faster than light: faster-than-light travel would be beneficial for space travel."
• "The axiom of choice must be wrong because it implies the Banach-Tarski paradox, meaning that geometry contradicts common sense."
• "Free will must exist: if it didn't, we would all be machines." (This is also a false dilemma.)
• "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.
• "Objective morality must exist; if it didn't, then it could be considered acceptable to commit atrocities."
• “The existence of gravity would make falling from a height onto a hard surface unpleasant, therefore gravity cannot exist.”
• “It can never happen to me. If I believed it could, I could never sleep soundly at night.”
• “I don't think that there will be a nuclear war. If I believed that, I wouldn't be able to get up in the morning. I mean, how depressing.”
• In “The Matrix,” Neo is asked whether he believes in fate; he says that he doesn’t. He is then asked why, and replies, “I don’t like the thought that I’m not in control.” This is not an appeal to evidence, but to the unpleasantness of believing in fate: Fate would imply that the world is a way that I don’t want it to be, therefore there is no such thing.