Ed. note - I apologize if you read it in the few hours that it was live as an incomplete draft; it probably made even less sense than it does now!
"I have never really understood missionary zeal of any sort,” wrote a commenter on the blog Cosmic Variance in reaction to the zeal of both religious proselytizers and Dr. Richard Dawkins, a geneticist and the author of The God Delusion, a book that attempts to demonstrate both that the existence of God is exceedingly improbable (for all intents and purposes, effectively impossible) and that religion, on balance, is bad for humanity and the individual.
The idea of missionary zeal can be basically defined as the determination to convince other people of your own point of view. Since missionary is a word loaded with religious associations, I think a better term could be found, but I've not been able to come up with one. The best I can manage is "activist" zeal, a term I will use in this post interchangeably with "missionary" zeal.
Regardless of whether or not the commenter meant to imply that all types of missionary zeal are the same (and he may not have been implying such), I think it may be useful to point out that differences exist, of course, and that the lack of such zeal entirely in the world would carry consequences.
The activist zeal of a Richard Dawkins or a Sam Harris (pictured, right) is based on evidence that is verifiable; it is not based on theology.
Those who proselytize (such as many evangelical Christians), cite the pending eternal damnation of the souls of the un-converted (or in the case of some Muslims cite other things, such as the impurity or evil of non-believers) as the reason for their missionary zeal (or in rare instances their homicidal zeal).
This reasoning, albeit ultimately circular, is sound within the rules of such a religious worldview that does not give physical evidence and scientific research as much weight when defining ultimate reality. It is a reasoning about ultimate truth that is often primarily based on claims or narratives in a holy book, as well as tradition or ancillary observations about a beloved religious tradition. (E.g., the evangelical Christian may embrace as true the notion that Jesus was born of a virgin; his or her proof will be limited to biblical citations, though he may also note that this belief is hundreds of years old, or that millions of people believe as he does--the implications being that therefore the virgin birth is true.)
Those who have activist zeal for countering such a religion-based worldview, that is, countering a worldview in which religious faith trumps what the scientific process usually recognizes as evidence, include people like Richard Dawkins (pictured, right), who are usually philosophical materialists to some great degree. Sometimes they are called "free thinkers" or "rationalists." For the purposes of this post, I'm going with the term zealous "rationalists."
When the issue is the existence of God, zealous rationalists often note that the scientific evidence for God's existence is practically nil, and that non-scientific evidence cited by the religious can be unpersuasive not only because it is not scientific, but because even as non-scientific evidence it looks unremarkable if compared to other non-scientific beliefs, including those now debunked or simply very unpopular. (E.g., To a Christian, a zealous rationalist might point out that Zoroastrians, who are rare but exist in pockets in southern Iran and mostly among the Parsi in India, also believe in hell, and then ask, "So if that part of Zoroastrianism--which incidentally pre-dates Christianity and Judaism--is true, what invalidates all other aspects of Zoroastrianism? Why not be a Zoroastrian?" Or a zealous rationalist might point out that the same holy book that is held up as evidence for Jesus' virgin birth also implicitly endorses slavery and contains factual errors, such as the erroneous belief that the sun orbits the Earth.)
When the issue is the harm religion can do, rationalists usually cite studies or--less convincingly, I think--cite moments in world history that can suggest that religious beliefs can be a root cause of or justification for violence (e.g. the September 11 terrorist attacks in the U.S.), for the suppression of liberties or rights (e.g. the institution of slavery among Christians in the 1800's and before), or even simply for some torturous fears an individual might suffer (e.g., the fear of a gay adolescent that he or she is demon-possessed or destined to go to hell).
The zeal of either type--the religious person or rationalist—might be considered distasteful by some. Perhaps by most. Yet, if no one ever had such zeal, some (many?) things most of us now deplore, such as slavery or even smoking, might be with us still. Improvements in things such as human rights and public health have in many instances throughout history not occurred without zealous people--including those who based their advocacy on theological grounds.
(Images: a mobile disaster relief vehicle of the Salvation Army and Medecins Sans Frontiers, a.k.a, "Doctors Without Borders" at work in Sudan.)
Whether or not all zealousness, as activism, is seen as annoying, it's true that not all zealousness is the same, and it is difficult to find motivations for missionary/activist zeal among rationalists that is not more humanistic than motivations for missionary zeal among the religious. For instance, Richard Dawkins' zeal is based on liberal, Western, humanist ideals including the goal of limiting human suffering. Conversely, the proselytizing zeal of most religious people is based on concepts about an afterlife or admonitions written in a holy book. Even when the religious are zealous not about proselytizing but about social justice (e.g., caring for the sick) because of an admonition in a holy book, their subsequent laudable actions are no doubt being executed also by many people without religious convictions at all.
Based on the above observations, I believe one should be more inclined to genuinely thank Dawkins than not to do so, to believe that his form of "missionary zeal" is better for us all than the missionary zeal of the religious among us.