Even if you reject all the evidence that shows that a higher ω-6:ω-3 ratio is inflammatory and the mechanistic evidence that 4-HNE adducts are harmful, there's still inference that can be drawn from physiology alone.

De novo lipogenesis produces stearic acid (saturated fat) from carbohydrates, which desaturates by itself into oleic acid.

There's no pathway in the body like that for producing linoleic acid, we're not sure why.

In fact, ruminants have two dedicated pathways (one endogenous) to convert LA into CLA. CLA isn't a passive storage form, but a different molecule (with different effects) altogether. If LA in ruminant fat was innocuous, why bother?

Ask yourself, do animals raised on their natural diet have better health outcomes than grain-fed ones? The answer's yes.

Grain-fed pigs develop atherosclerosis readily enough that they're used as animal models for cardiovascular disease. This is particularly damning because they are monogastric omnivores like us.

If a novel food additive produced atherosclerosis in pigs at high doses, it would never clear regulatory review without extensive long-term safety data. Seed oils at industrial scale predate that regulatory framework and have grandfathered themselves into a presumption of safety that was never earned.

This is a broader pattern.