Other Terms and/or Related Concepts
Is/ought fallacy; Argument to nature.
The advocate claims that because something is natural or exists in nature, it is by definition good. And/or the advocate derives 'ought' from 'is' without any compelling (and reasonable) link.
Talk show host Grant Haggard has invited guest Riley Hardge on his show to discuss proposed gay marriage legislation. Hardge, attempts to bring up Haggard's recent arrest for public obscenity: "So Grant, you admit you were in the park that afternoon, and given you had binoculars I would normally believe you when you say you were bird watching. But why did witnesses see you in your van with your pants off?"
Haggard ignores the questions, turns to the camera and states: "The issue at stake here is the nature of family and life itself. Enacting this legislation would be commiting a crime against nature. The natural state of affairs is for marriage to be one man and one woman, so we can maintain the family unit. Look no further than the humble beaver. Both mother and father beaver have essential roles in the family unit. They mate for life and raise their young together, as a team. Just like humans do!"
Haggard's argument is wrong in two significant ways. The first, and most obvious, is that he has cherry picked one example from nature, from millions, to make his point. He has Stacked the Deck. One can demonstrate this easily by picking a fun counter example. Bonobos, for example, exhibit almost the complete opposite behaviour to beavers. They are overly promiscuous, engaging in opposite sex, same sex, and multiple partner sexual behavour, as frequently as humans shake hands.
The other way in which he is wrong is the Naturalistic Fallacy. Giving his example the benefit of the doubt, let's say that in nature homosexuality does not occur besides in humans. So? There is no compelling logic or link from the way things are (a description) to the way things ought to be (an ethical position). Haggard is essentially Begging the Question. He has presupposed that the way beavers live is good.
Another example of the Naturalistic Fallacy is the most basic argument in favour of Social Darwinism - a theory of societal ethics which claims its basis is in nature (evolution by natural selection - though it has a closer resemblance to selective breeding). Social Darwinists argued that if nature is this way (only the ‘fittest’ survive), then it ought to be this way with various features of society. (It has been mostly used as a justification for laissez-faire economics and eugenics.) But as with the previous example, this is an unfounded leap.
An argument in support of an ethical theory needs a better claim than, because something is done this way, it ought to be. This has nothing to do with whether it is right or wrong, good or bad. It is simply a statement of (supposed) fact. To get from a fact to an ethical value, there needs to be some kind of compelling argument about the ‘goodness’ or ‘evilness’ of the fact. For this to happen we need an agreed upon ‘good,’ and an agreed upon ‘evil’. (Note, this is a very simplistic treatment of Social Darwinism - and arguments not based on ‘is-ought’ with respect to the ‘goodness’ of laissez-faire economics and eugenics have been made by many.)