If the doctors can't find concensus over butter, how can they recommend aspirin? Or ibuprofin?

While medications (prescription and over the counter) arguably have a dark cloud hanging over them and the shady tactics these pharmaceutical companies employ through their lobbying and political donations, they are tested and regulated to a certain degree.

To my knowledge, the only thing tested in butter is the dairy component. We know that the two key ingredients in a good butter are cream and salt. Most of the fat in cream is saturated fat and it is really bad for you. Too much salt is also bad for you. Even if you consume unsalted butter, you're still consuming saturated fat from the cream.

So to really answer your question, the ingredients are tested and many studies have been done on saturated fat, cream and salt over the years. The answers keep on changing, we keep being told something is good and then bad, then good again. The components in butter are probably better tested than aspirin or ibuprofen.

At the end of the day, nothing is good for you in excess. If you drink too much water you'll die, eat too many greens like spinach and you'll poison yourself. Take aspirin too much and it has been proven to have serious side effects like internal bleeding.