Contraindications and/or "toxic" oils.
Get five books by different people, all well-respected in their field, and there will be at least one oil on each list that isn't on any of the others.
At least one oil will be used in each book that the other four have screaming tizzys over the very idea of. Eventually, if you read enough books, you'll have such a list of potential "problem" oils that you'll be scared to use olive oil on your salad.
There are oils that are supposedly "OMG never even think about using this!" that I use regularly with good results.
There are oils that I use neat or -- horrors! -- drink in water or juice. According the the American health system, this is an extreme no-no, though this method has been in use in Europe for years.
My suggestion? Do the research, test the oils, and make your own decision!