people who cook their own food are at least aware of the amounts of oil/butter/whatever culprit you want to claim (salt? sugar?). when you eat fast food, you ha

people who cook their own food are at least aware of the amounts of oil/butter/whatever culprit you want to claim (salt? sugar?). when you eat fast food, you have no idea how much of these ingredients you're consuming (usually more than you would have used if you had made a similar meal yourself) and they're often labmade replacements with unclear side effects (for example, during the fat-free craze of the early 00s, a commonly used additive (olestra) ended up causing anal leakage and ended up being illegal in several countries). butter won't do that.