What a confusing topic our spreads have become.
Margarine was first invented with the intention of developing a product healthier than butter. In the late 1960's when studies found people who had high cholesterol were having more heart attacks, the food science community went about trying to lower the cholesterol intake of consumers. Since butter contains cholesterol, the search was on for a substitute.
Cholesterol is a naturally occurring fat in all animals. It's made in the liver and does serve some good purposes (it's a precursor to vitamin D). But too much can clog our arteries and lead to heart and artery disease.
So the bright idea was to take corn oil, which is cholesterol free (as are all plant oils) and make a yellow stick of spread out of it to mimic the butter we love.
A decade or so later, scientists found that cholesterol in the diet is not, in fact, the primary cause of elevated cholesterol levels in the blood. It's saturated fats (those solid at room temperature) that are responsible for raising the levels of so-called bad cholesterol.
Fortunately, there are many other options available. While I wouldn't choose a stick of margarine over a stick of butter, margarine comes in many forms that are more healthy because they are less solid. A tub of margarine is more healthy than a stick because it's less saturated (you can tell because it's softer). The squeeze margarines are still more healthy (more liquid, less solid). The spray margarines are best of all if you're watching your blood lipids. The simple rule is, the more liquid (the less solid) the better these are for your cholesterol levels.
Many of the less-solid forms are also lower in fat and Calories too--and we're always watching our calories!