Butter is actually a very healthy food.
"In addition to vitamin A and E, butter contains vitamin D which is essential to the proper absorption of calcium and therefore necessary for proper bone growth and the development of healthy teeth. The rising rates of osteoporosis in milk drinking western nations may be due to people choosing skim milk over whole, thinking it is better for them. Butter is also protective against tooth decay.
Butter is one of the few foods that supply an adequate amount of iodine in a highly absorbable form. Iodine is critical for proper thyroid functioning as is vitamin A.
Cholesterol in butterfat promotes health of the intestinal wall and is protective against cancer of the colon. Glycospingolipids, a special category of fatty acids found in butterfat, is protective against gastrointestinal infection. Children who drink skim milk have diarrhea rates three to five times higher than children who drink whole milk. Butter's short and medium chain fatty acids have a strong anti-fungal effect and play a role in the treatment of candida overgrowth.
Butter contains small but nearly equal amounts of omega-3 and omega-6 essential fatty acids. This excellent balance between linoleic and linolenic acid helps prevent the problems associated with excessive consumption of omega-6 fatty acids."
Butter is also an agent of weight loss. Read more here