Butter isn’t bad for you per-se, it’s the quantity that gets you. It’s a pretty calorie dense food, and it has a lot of other things in it that, when taken in large quantities will clog up your cardiovascular system.
Used in proper moderation and it’s wonderful. Throwing a whole stick of it into a single serving at every meal is probably too much.
Disclaimer: I am neither a health professional, nor a nutritionist.