I havn't researched it that much, as I use margarine sparingly, I've never seen it as much of a concern. It seems everything is bad for you.
The bottom line is that butter is a whole food and is loaded with vitamins, minerals, and healthy fats, whereas margarine, though often marketed as a healthy alternative to butter, is loaded with nasty trans fats which only do harm to the body. The only feasible reason for a person avoiding butter is that they're vegan or don't consume dairy products. But even myself, being someone who avoids most dairy, can say that butter is one of the better, healthier dairy products, but only if the butter comes from grass-fed cows not treated with hormones and antibiotics.
I am, it's a testament to my superior taste and drive to discover unheard masterpieces. A labor of love which goes almost entirely unthank'd.