Man: What was the cause of the Civil War?
Apu: Actually, there were numerous causes. Aside from the obvious schism between abolitionists and anti-abolitionists, economic factors, both domestic and international ...
Man: Hey, hey!
Man: Just say slavery.
Apu: Slavery it is, sir.
— The Simpsons, “Much Apu About Nothing”
In my experience, many people, from across the political compass, are resistant to considering the possibility that a given phenomenon might have multiple causes.
You meet someone who has a broken arm. How did that happen? Every broken arm you're aware of has been the result of someone having an accident on a two-wheeled vehicle. So you say to them, “Sorry you've got a broken arm - two-wheeled vehicles are dangerous, eh?” To me, that's a clear fallacy.
Why do people develop Chronic Fatigue Syndrome? Well, as a _syndrome_[a], it merely represents a collection of symptoms, rather than a disease with a single well-defined aetiology. Just because thing X₁ cured a particular person's CFS, doesn't mean that will be the cure for every person with CFS. Yet if one has tried X₁, X₂, X₃, etc., and none of them produced any significant lasting[b] result, there can be a ‘diagnosis’ which assumes there can't be any other possible causes, and that one's CFS must be purely psychological in origin.
Why am i nonmonogamous? Genetics, epigenetics, environmental factors? i'm open to the possibility that it's any one of these, or any combination of these. But who can say for sure without knowing both the entirety of my genotype and every detail of my life history? Even if humans in general are ‘naturally’ monogamous - and biological arguments can be made that we're not[c] - that doesn't necessarily mean that every individual human is ‘naturally’ monogamous; that seems to me to be an ecological fallacy.
Occam's razor is often appropriate. But i would suggest that caution is required when applying it to highly complex dynamic systems like humans. Just because a certain narrative feels ‘truthy’ on the basis of one's ideological prejudices, doesn't mean it's actually wholly true.☙
[b] The word ‘lasting’ here is important. A number of people with CFS undertake a particular course of treatment and initially experience what seems to be a significant improvement, yet in the longer term find their health “regressing to the mean”.
[c] Cf. e.g. “The Myth of Monogamy”, by David P. Barash and Judith Eve Lipton, who argue that humans should practice monogamy despite it not being biologically ‘natural’ for us to do so.