There are so many reasons not to eat margarine. Sure, it's soft and tastes "buttery", and it's cheaper than butter, but c'mon folks, it's nothing but chemicals. I'm starting to employ the logic that if I don't know what the ingredients are, then I shouldn't eat it. Here is the wikipedia article on margerine, which is very factual, based on the food research that I've been conducting the past few years.
Not only is my challenge an effort to go green, but also one to eat healthier, more in line with what is good for the planet is good for the body.
Growing up, my mother only bought margerine. It came in a tub, which we used on our toast, and in stick form, which she would use for baking. Only when company came for holidays would she buy a stick of butter to place in the butter dish on the table, to be used on the mashed potates and rolls. I remember eating this butter and feeling that it was a very special thing, as it was only served at holidays, much like the good china was used at these meals.
5 years ago when I started cooking for others and really getting into the art and science of food, I became a purist, and while I would still have margerine in the house for bread, butter was the only acceptable thing for cooking and baking. Now, I'm giving up margerine altogether. I just purchased a butter bell on ebay (until then my butter is sitting on a plate on the kitchen counter), and I'm quite pleased to have eliminted another source of chemicals from my life.