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Logic and rhetoric
A moralistic fallacy (often, wishful thinking) is a logical fallacy that occurs when someone asserts that the way things should be is in fact how they are.
While cognitive dissonance (e.g. as in the fable of The Fox and the Grapes) describes the suffering experienced when holding an internally inconsistent worldview, utilizers of the Moralistic fallacy solve this discomfort by simply overwriting everything with how it should be, case closed - ta-daa, suddenly the world adds up.
- wishful thinking
- appeal to hope
Wanting something to be true is irrelevant to its truth. However, if this belief were true, our wishes would always come true. Clearly, this is not the case.
Don't believe us? A toddler can't desire a cookie into existence; 6 million Jews couldn't desire themselves out of death camps.
The term "moralistic fallacy" was coined by biologist Bernard Davis, who was upset about how, in his opinion at least, biology was unable to do significant research into behavioral genetics. The reason being that on one side, racists and the like are always searching for some way to hide their bigotry behind science; "we aren't racist, we're race realist and have this poorly defined study to back us up!" It's to the point where if someone starts up about group genetics and behavior/intelligence/whatever, 11 times out 10 you are going to hear a racist diatribe. Never mind that if any "race" is the "master", it's the mixed race; there's reasons most species reproduce through sex and not cloning.
Counter to this, and the focus of Davis's ire, are progressives and rights activists who insist that because bigotry is wrong, anything that could possibly be used to support the idea that any differences between people are inherent rather than social or environmental must also be wrong, including behavioral genetics. It certainly didn't help that the same guy who founded behavioral genetics is more famous for creating Eugenics. So while the various racists commit moralistic fallacies with regards to biology and genetics, progressives may commit the moralistic fallacy and impede research whether it's for the "right" reasons or not.
- PETA and other animal rights activists have argued that milk is less healthy than alcohol, and even causes autism in the unborn.
- Some feminists may go beyond merely saying men and women ought to have equal opportunities to asserting that they do everything equally well, or that women do everything better.
- Some vegans will claim that humans don't naturally eat meat or that our digestive systems can't handle it, which if true would cause meat eaters to be emaciated rather than obese...
- Infidelity is viewed as immoral by many, and so it must not be natural to desire other people than one's monogamous partner.
- Some fundamentalists' statements about Darwinism or homosexuality (which, in that latter case, also use the reverse).
- The vast majority of alternative medicine (especially of the "indigenous" variety) follows this line of logic.
The concern has been that evidence contradicting such moral values will lead to people justifying this behavior, since it is "natural". While understandable, this has led to instances in which research that contradicts them caused people uncomfortable with it to engage in denialism. In the realm of religion it can take the form "God is good, therefore He does not support X, which I view as bad." Alternately, it is possible for an atheist to make the opposite fallacious argument (as they are alleged to by some theists) that "I view God (or His commands) to be bad, therefore He does not exist."
In public policy
Wishful thinking may characterize popular consensus on other important public policy issues. For example, American space policy is now in the grip of the belief that private firms will finance the exploration of outer space. For a while this seemed unlikely, but felt good because it offered an escape from spending the large sums necessary for human space exploration. (However, it should be noted that, while space exploration is expensive, it forms a much smaller part of the national budget than most people realize: NASA's share in the US budget comes to around 0.6%, down from around 5% during the height of the Apollo program.)
It should be stated, however, that this example may in fact become a reality. Elon Musk's SpaceX appears on the verge of bringing reliable, reusable rockets into the mainstream, promising to cut the cost of space missions by orders of magnitude. Other firms including Planetary Resources and Deep Space Industries were founded with the intent to (eventually) mine asteroids and ship the products around the solar system; even if reusable rockets become commonplace, building space hardware without having to rocket raw materials out of a gravity well is hoped to be substantially cheaper.
If this actually happens, we'll need a new example. Humans being the delirious life forms we are, though, there should be no shortage.
Positive outcome bias
Positive thinking versus wishful thinking
Wishful thinking is not the same thing as "positive thinking," or the idea that by thinking positively, one will experience better outcomes. Thinking positively can help a person achieve a particular goal, in much the same way that thinking negatively can be a demotivating factor; thinking positively can conceivably help someone to maintain their focus on getting some task done. Wishful thinking, on the other hand, is more about changing reality to match your perceptions, or thinking that reality would be swayed by what you think.
An apt analogy can be found in medicine. Thinking positively about a course of treatment can improve a patient's outlook on life, helping the patient to feel better and maybe even having a placebo effect. Meanwhile, wishful thinking would entail denying that one had an illness, or that God would cure it, or that it will simply get better on its own, and assuming it would go away just because of that.
- Appeal to nature: What is natural is good.
- Hume's law: The is/ought problem.
- Solferino fallacy: War is natural, and therefore good.
- Wishful thinking
- Appeal to consequences
- Appeal to emotion
- Escape to the future
- Word magic
- Law of Attraction
- Magical thinking
- Willful ignorance
- Logical Fallacies.info on the moralistic fallacy.
- Iron Chariots on the moralistic fallacy.
- Fallacy Files 
- Internet Encyclopedia of Philosophy 
- Wikipedia 
- Bruce Thompson 
- Global Tester 
- Skeptic's Dictionary 
- Gordon, Hanks, & Zhu