Re: Olive oil
It's fine to use olive oil for cooking or frying up to a certain temperature. After that it ruins the flavour and it's not much use for deep fat frying. It also depends on how much oil you use. IMO if something tastes bad then it's not good for you.
There's so much conflicting information about different oils but all frying is bad for you if that's all you eat. Baking is bad too for different reasons. Grilling meat can cause cancer chemicals even if you don't use oil. Burnt toast is cancer chemical ridden. Nothing that is nice and interesting to eat is really 100% safe.
I like to cook at a lower temperature not because I am worried about cancer but because food comes out tasting better. I'd say butter is the worst for frying, but it tastes pretty good for an occasional treat.
It is really down to how much and how often you eat the things that are not good for you rather than them being bad for you. For example they say you shouldn't eat smoked meat because of the nitrates content but there are people who live to 100 having eaten it regularly. It's more to do with the type of body you have (genes) and the rest of your diet/lifestyle.