I'm not massive on either to be honest as I don't eat much bread, but I do find evangelical Butter snobs a bit over the top. Probably because I had a friend who had a similar reaction to you when I first met him and as I spent more time with him he came out with even more outlandish claims about food that didn't seem to have much substance in reality.
I went on a nutrition course a while back by the NHS through work. It's been a while since I did it, but I remember they were pretty inconclusive around butter/marge.
If it's on taste alone that's fair enough.