The moralistic fallacy is the formal fallacy of assuming that what is desirable is found or inherent in nature. It presumes that what ought to be—something deemed preferable—corresponds with what is or what naturally occurs. What should be moral is assumed a priori to also be naturally occurring.
The moralistic fallacy is in essence the reverse of the naturalistic fallacy.
Steven Pinker writes that "The naturalistic fallacy is the idea that what is found in nature is good. It was the basis for Social Darwinism, the belief that helping the poor and sick would get in the way of evolution, which depends on the survival of the fittest. Today, biologists denounce the Naturalistic Fallacy because they want to describe the natural world honestly, without people deriving morals about how we ought to behave -- as in: If birds and beasts engage in adultery, infanticide, cannibalism, it must be OK." Pinker goes on to explain that, "The moralistic fallacy is that what is good is found in nature. It lies behind the bad science in nature-documentary voiceovers: lions are mercy-killers of the weak and sick, mice feel no pain when cats eat them, dung beetles recycle dung to benefit the ecosystem and so on. It also lies behind the romantic belief that humans cannot harbor desires to kill, rape, lie, or steal because that would be too depressing or reactionary."
- Warfare is destructive and tragic, and so it is not of human nature.
- Eating meat harms animals and the environment, and so no one has physiological use for it.
- Men and women ought to be given equal opportunities, and so women and men can do everything equally well.
- Unfaithfulness is immoral, and so it is unnatural to feel desire for others when in a monogamous relationship.
- A universe without a lawgiver would have no basis for morality—which would be a ghastly state of affairs—and so God must exist.
- Warfare must be allowed because human violence is instinctive.
- Veganism is folly because humans have eaten meat for thousands of years.
- Men and women cannot have the same roles in society because men have more muscle mass and women can give birth.
- Adultery is acceptable because people can naturally want more sexual partners.
Effects on science and society 
Sometimes basic scientific findings or interpretations are rejected, or their discovery or development or acknowledgement is opposed or restricted, through assertions of potential misuse or harmfulness.
In the late 1970s, Bernard Davis, in response to growing political and public calls to restrict basic research (versus applied research), amid criticisms of dangerous knowledge (versus dangerous applications), applied the term moralistic fallacy toward its present use.
(The term was used as early as 1957 to at least some if differing import.)
In natural science, the moralistic fallacy can result in rejection or suppression of basic science, whose goal is understanding the natural world, on account of its potential misuse in applied science, whose goal is the development of technology or technique. This blurs scientific assessment, discussed in natural sciences (like physics or biology), versus significance assessment, weighed in social sciences (like social psychology, sociology, and political science), or in behavioral sciences (like psychology).
Davis asserted that in basic science, the descriptive, explanatory, and thus predictive ability of information is primary, not its origin or its applications, since knowledge cannot be ensured against misuse, and misuse cannot falsify knowledge. Both misuse and prevention and suppression of scientific knowledge can have undesired or even undesirable effects. In the early 20th century, development of the basic science quantum physics enabled the atomic bomb through applied science in the mid 20th century. Without quantum physics, however, much technology of communications and imaging, by other applied science, could have been renounced.
Scientific theories with abundant research support can be discarded in public debates, where general agreement is central but can be utterly false. The obligation of basic scientists to inform the public, however, can be stymied by contrasting claims from others both rousing alarm and touting assurances of protecting the public. Davis had indicated that greater and clearer familiarization with the uses and limitations of science can more effectively prevent knowledge misuse or harm.
Natural science can help humans understand the natural world, but it cannot make policy, moral, or behavioral decisions. Questions involving values—what people should do—are more effectively addressed through discourse in social sciences, not by restriction of basic science. Misunderstanding of the potential of science, and misplaced expectations, have resulted in moral and decisionmaking impediments, but suppressing science is unlikely to resolve these dilemmas.
Seville Statement on Violence 
The Seville Statement on Violence was adopted, in Seville, Spain, on 16 May 1986, by an international meeting of scientists convened by the Spanish National Commission for UNESCO. UNESCO adopted the statement, on 16 November 1989, at the twenty-fifth session of its General Conference. The statement purported to refute "the notion that organized human violence is biologically determined".
Some, including Steven Pinker, have criticized the Seville Statement as an example of the moralistic fallacy. Research in the areas of evolutionary psychology and neuropsychology suggest that human violence has biological roots.
See also 
- Q&A: Steven Pinker of 'Blank Slate', United Press International, 10/30/2002, http://pinker.wjh.harvard.edu/books/tbs/media_articles/2002_10_30_upi.html
- Davis BD (1978). "The moralistic fallacy". Nature 272 (5652): 390. doi:10.1038/272390a0. PMID 11643452.
- Moore EC (1957). "The Moralistic Fallacy". The Journal of Philosophy 54 (2): 29–42. doi:10.2307/2022356. JSTOR 2022356.
- Davis BD (2000). "The scientist's world". Microbiol Mol Biol Rev. 64 (1): 1–12. doi:10.1128/MMBR.64.1.1-12.2000. PMC 98983. PMID 10704471.
- Kreutzberg GW (2005). "Scientists and the marketplace of opinions". EMBO Rep 6 (5): 393–6. doi:10.1038/sj.embor.7400405. PMC 1299311. PMID 15864285.
- Davis BD (2000), section "Technology".
- Davis BD (2000), section "Limited scope of science".
- Suter, Keith (2005). 50 Things You Want to Know About World Issues... But Were Too Afraid to Ask. Milson's Point, NSW, Australia: Transworld Publishers. ISBN 978-1-86325-503-5.
- Pinker, Steven. How the Mind Works. New York: W. W. Norton & Company, 1997.
- Jones D (2008). "Human behaviour: Killer instincts". Nature 451 (7178): 512–5. doi:10.1038/451512a. PMID 18235473.
- May ME & Kennedy CH (2009). "Aggression as positive reinforcement in mice under various ratio- and time-based reinforcement schedules". Journal of the Experimental Analysis of Behavior 91 (2): 185–96. doi:10.1901/jeab.2009.91-185. PMC 2648522. PMID 19794833.