I submit that, especially with the enhanced communication abilities in the modern world, the repeated failure of these doomsday prophets will result in less religiosity and more atheism. Therefore, rather than seeing these "scary" predictions as noble lies to help win souls for christ, the reality is that these people are likely causing more people to laugh at and turn away from religion.
These individuals making or following various cultish predictions concerning doomsday appear sincerely to believe their claims, but they demonstrate that they have little regard for moral responsibility. That is, they have not thought about the consequences of their actions and how their overtly displayed, and embarrassing false certainty will lead others to become less religious. If "soul-winning" is a noble thing, according to their their faith tradition, then losing souls must not be looked upon too favorably from on high. While I know this won't deter people the very next day from making new false predictions, they should at least consider the moral irresponsibility of their actions.
For atheists, these false predictions should be an
god-send. Unfortunately, many atheists don't seem to know how to capitalize on such things. Believers will just shrug this off and go on to believing the next dubious prediction tomorrow, not even remembering the trail of false hopes an vain claims their their religion has lead them into. Perhaps atheists need to make a bigger deal out of such things. Perhaps they should have a special word for when doomsday predictions fizzle and gloom and doom go kaboom. I have proposed some candidate terms like "dumbsday", or "dudsday", or "dundersday". Instead of a prediction, one might have a "predorktion" to describe the phenomenon when the prophets boff-it. At the very least I think that a secular group like American Atheists should hand out an award called the "NostraDumbAss Award", to failed prophets, and people like Harold Camping should be this years nominee.
Perhaps it would fun to make a t-shirt with a list of failed doomsday prophecies, each one being exed out, and a few that are yet to come, such as 2012, and a few blank spaces that say