My stance has always been that butter is so delicious that I am willing to accept a reasonable amount of risk, whereas I find margarine so foul that I would rather eat food without any fat than consume it.
Amusingly, I quit butter for that reason. I had a major health scare just over a year ago, and despite being skeptical of dietary advice in general, I decided that at least I could lose weight. So I cut butter out of my diet. The result was that I ate a lot less food overall, because it eliminated most of my favorite snacks, such as buttered toast. Sure, I missed it, but I've gotten slimmed down, and am having no problem keeping it off so far. It took months, but the day arrived when I actually enjoyed a piece of toast with no butter!
So, this has more to do with me hacking my own brain, than about any sort of nutritional science.
In my case, I lost the weight by eliminating a lot of carbohydrates from my diet. The only way I would bother touching a piece of bread would be if it was unusually delicious.
