During debates regarding various moral issues one often hears a certain kind of argument which might go like this:
Action X is unnatural / artificial therefore it is morally wrong.
Action Y is Natural / normal therefore it is morally right
This line of thought is a well known mistake of reasoning which is labelled as the "Naturalistic fallacy" . A naturalistic fallacy occurs when the arguer asserts that since something is unnatural therefore it is immoral . However the rightness or wrongness of an action has nothing to do with how the world in fact is (factual) . Morality pertains to the ideal world i.e regarding how it ought to be (prescriptive). Right or wrong are prescriptive statements not factual ones . For example even if human beings infact behave selfishly doesnot mean that we ought to behave selfishly.
we can easily think of a lot of counter examples to show that this form of reasoning is a fallacy:
Consider the example of unnatural and artificial behaviours that we all treat as morally good if not necessary. Clothing is not naturally grown on our body , it is an natural act that we mould materials to cover our body. similarly Housing is not naturally grown out of the ground . We artificially construct them. Again , when we perform a heart transplantation surgery we are committing one of the most unnatural acts one could ever perform . Yet all of these would never be judged as immoral (atleast by sane people) . Infact in order to truly live naturally we would have to go back to living like cavemen using self crafted bows and spears to hunt.
Similarly , consider instance of natural events that all of us would judge as immoral had they been committed by a human agents : cancer, premature death (or any form of death infact), natural disasters. Clearly no one will argue that since all these events are natural therefore they are also morally preferable in the sense that we should encourage there occurrence and even celebrate them. Similarly suppose it was discovered that paedophilia is genetic i.e. some humans are by there very nature attracted to children , such a discovery would mean that paedophilia is completely natural but that obviously that doesn't mean that paedophilia would therefore be morally admissible .
One common instance of this fallacy is when evolutionary biology is forced onto how we ought to behave : for example arguing that since evolution follows the principle of "survival of the fittest" therefore it follows that any evolved species must also follow similar rule in its moral consideration (i.e. Social Darwinism) . Clearly this doesnot follow . Another instances of when Marriage Equality is resisted based on the fact that "its not natural".
Let us stop extracting morality from how things really are and focus on how things ought to be like.
PS: for a more detailed exploration of this fallacy see this.