My understanding is that the impurities are contained not in the oil part of the butter, but in the milk part, the part you skim off when you make the ghee. If you find making ghee laborious it can be bought in Asian/Indian food stores.

Also, by making your own, you can choose butter from a so-called organic dairy, where I think the quality is higher, and the animals treated better. At least, I sure hope so.

Now, I'm going to go and do some research on ghee. I like the fact that it is a traditional product from an old culture; trad. peoples, while not perfect and making mistakes like everyone else, had a way of separating out the good from the bad through trial & error over centuries.