I would not substitute olive oil for butter in all cooking situations. The problem is that olive oil, regardless of the purity and quality is not stable at high heat. Whereas butter is. So if you use olive oil to saute vegetables, for example, you will overheat the olive oil, resulting in dangerous chemicals in your food. My rule of thumb is that olive oil should be used at room temperature and up to the temperature of boiling water.

This means it is OK to use olive oil when cooking soups, for example. But I never use it above that temperature. If I want olive oil in a disk for either taste or health reasons or both, and the dish needs to be cooked at temperatures above that of boiling water, I simply add the olive oil when the cooking is done and as the dish is cooling.

The only two oils I kow for sure are safe above the temperatujre of boiling water are organic butter and organic coconut oil. There likely are others, but more research is needed to be certain they are stable at the higher temperatures.

Many will likely disagree with my statement about olive oil, but I have seen the chemical research and am convinced it is accurate.