In my opinion, it's not seed oils as such that are the problem, so much as _any_ refined oil. We evolved for a hundred million years or more consuming foods containing oils. But the refined versions of the same oils are a problem because 1) we didn't evolve (at least not for 100 million years!) consuming them on their own, without the fiber, complex carbohydrates, and other elements that naturally accompany them, and 2) it's just too easy to eat too much of them when they're refined, since we like the taste.