Every now and then someone, outside and even inside the Esperanto movement, steps forward and accuses those who promote the language of displaying "religious fervor" or engaging in "sectarianism".
I can't argue with the phenomenon, which I've seen, and even participated in, over almost half a century. But the description is, IMHO, not nearly accurate.
"Religious fervor," for instance, might better be called "I've-got-a-good-idea-and-why-aren't-you-listening-to-me?" fervor. "Sectarianism" would be better labeled "The-world-is-divided-into-two-groups-and-we're-one-of-them"-ism. As far as I can tell, these are normal human behaviors, not limited to any particular religion or to religion in general. You can find them among Jehovah's Witnesses, people who dress up in Starfleet uniforms and attend conventions, people who believe that the world would be better off with an easy-to-learn common language, and people who believe that smoking is bad for you.
So why do we normally associate them with religion? Well, let's grant that the labels I suggest above are a bit overlong, and let's also recognize that these modes of behavior are, in our society, most often manifested in a religious context. So it seems natural that we would automatically label such behaviors are religious; that is, after all, where we primarily notice them. But, again, let me emphasize that they are not restricted to religious enthusiasts and are, in fact, fairly normal reactions to a society that evinces (in the best case) indifference and (in the worst case) hostility to an idea that you know is a good one.