Now, here's a horrible example of religious fundamentalism: A wanna-be-holier-than-thou vegan mother starves her baby to death by refusing to breast-feed him.
It seems that you can ruin almost any ideology or philosophy by turning it into a religion. That is, ignore the basic reasoning behind the idea and just concentrate on adhering to the "dogma" as literally and absolutely as possible. It is easy to chant a slogan such as "milk is murder" but it seems to require at least an average intelligence to understand what it actually means.
And by the way, I've personally been a vegetarian my entire lifetime.