Let’s simplify a bit. 

Most fats are a good nutrient dense food. 

Id venture to say that even seed oils when raw aren’t *that bad.  (Flax, grapeseed)
The bigger problem is the way they process them in bulk damages them.  “Cold pressing” uses no heat so it remains raw but is expensive to do with large quantities of seeds so instead they boil and separate the fat out. 
This damages the oil and effectively makes it rancid in the body. 
You should never heat an oil past its smoke point. (Even tallow)

*As a general rule avoid seed and vegetable oils.  (Corn, Canola)
Nature develop interesting ways of discouraging foraging animals from eating their seeds.  (Toxins)
A fruit that contains seed is different, the plant is using the yummy fruit as a way of disbursement. (Olive, avocado)

Always Buy cold pressed.

Omega-9 and Omega-6 are delicate. should be eaten raw and not exposed to heat.

Do a quick search when barbecuing or broiling as to not exceed smoke point temps.