In the early 1800s, people believed that organic compounds (chemicals associated with living processes) were fundamentally different to inorganic ones. They thought that such compounds were imbued with a sort of life-force, and that man would never be able to replicate them.
Friedrich Wohler upset everybody by synthesizing urea (by accident). People then realised that although organic compounds have some interesting properties - based as they are on carbon, which is a rather unique element - they're still just chemicals, and you can synthesize them like anything else. There's no magical distinction between, say, urea that you extract from animal urine, or the same molecule made in the lab.
Dieticians, as usual, are about 200 years behind the cutting edge of science. They still believe that some mysterious factor distinguishes the palmitic acid that you ingest (the most common saturated fatty acid in natural foods) and the palmitic acid that your body synthesizes for itself, as an energy storage/transport medium.
The former will apparently give you heart disease if gets into your bloodstream. The latter ... well, it's a bit hard to accept that your body would expend effort on synthesizing something that, as soon as it's released into your bloodstream, causes heart disease; and if it does cause heart disease in the same way as dietary saturated fat, it's even harder to accept that evolution or The Creator would come up with such a boneheaded scheme.
The only remaining conclusion is that the palmitic acid that you ingest, and the palmitic acid that your body makes for itself, are two different things. One is poison. One is harmless. Despite the fact that they're chemically identical and are, indeed, made by the same process (the fat you ingest from, say, a pork chop was created by the same chemical pathway that your body uses ... albeit inside a pig).
Anyway, if you can accomodate that feat of doublethink, it's all downhill from there. Saturated fat in your diet "causes high cholesterol", and that causes heart disease. But since saturated fat that your body makes is harmless, you can eat as many carbohydrates as you like. Your body will convert much of those excess carbs to palmitic acid for storage. But that's OK, because only the palmitic acid that you eat is a problem!
You're probably losing the thread at this point, unsure whether I'm serious or just extracting the urea. Unfortunately, it's both. This is what the medical profession actually believes to be true. And their solution to it is inevitably illogical: just like the medieval leech-merchants who believed we had "too much blood" that needed removing, the modern doctor thinks we have "too much cholesterol" that must be removed. The difference is that leeches, on the whole, were fairly harmless. Statins ... not so much.
I honestly don't know how this sort of thing happens. But I fervently wish that it didn't.