In the book “Primal Body, Primal Mind” there is an incredible chapter on why vegetable oils are so harmful. I never knew why until I read that. Basically, the way they are extracted damages the oils horribly, even if it says “cold pressed” because there are like 20 additional steps it has to go through to get extracted. By the time the oil is bottled, the author says it is GUARANTEED to have significant amounts of trans-fat in it.
So that was enough for me to avoid them like the plague, especially when there are many more healthful oils out there (coconut oil, olive oil, avocado oil). The poly-unsaturated oils have much more potential to be damaged because of their structure, than mono-unsaturated oils (olive oil) or saturated fats.