My gut instinct is that seed oils are probably bad, but I don't have hard evidence of this. Instead, I see them as a proxy for highly processed foods. Usually it's pretty accurate: If you find a seed oil in the ingredients list there's a good chance you'll also find other nasty stuff like HFCS, various preservatives, added sugar, and so on. Real food doesn't need seed oils and often times it's added for the benefit of the processing machines rather than the food.
Eat real food, avoid processed crap, and you are 99% of the way there.