"Seed oils and sweeteners" are two radically different things. Do you think there's some common underlying mechanism, or that both just happen to be bad in completely unrelated ways which somehow both have the same result of encouraging weight gain?
but there are lots of other seed oils that have become much more popular in the last half-century that are more plausible suspects, like cottonseed oil, sunflower seed oil, and safflower oil
i think rapeseed oil is probably not it because its popularity is more recent
there was a lot of excitement about ten years ago that the ratio of n-6 unsaturated fats to n-3 unsaturated fats might be the key, but that doesn't seem to have panned out
the fact that somebody else might be allergic to it doesn't seem like a major consideration for whether i should cook with it though
unless they're coming over that day