Three of the most powerful weapons against theism and other irrational beliefs
In no particular order:
1: Education. When you learn how evolution works, and how we know it works, you are no longer able to honestly deny it's facts. When you learn the earth is round, and how we know it is round, you can not honestly deny it is round. An education may not stop a liar from denying reality, but there aren't that many people who actually enjoy lying once it's been pointed out that they are lying. A theif's worst enemy is recognition.
2: Diversification. I have little to nothing in the way of hard evidence of this position, merely personal experience. I'm unaware if large and/or long term studies have been done on the issue, though would recommend that they be done by those capable of doing them. But in my experience, irrational viewpoints become harder to sustain when not surrounded by those who share them. Racism in a small town full of caucasian people(merely an example) is, in my experience, far more common than in a large city with multiple ethnic groups. Religious beliefs in a small town of one ethnic group are far more centralized than in a large city of dozens of them. I don't think everyone needs to be living in cities, but I do think that minorities need to spend more time getting into small communities; and that majorities need to spread out more so as not to be such a majority. How much harder is it to recruit extremists when you're surrounded by people who believe something other than what you believe?
3: Ridicule. People who believe in alien abductions don't tend to admit their tales(more than once). Whether or not they believe the abduction happened, the majority of society laughs at their claims. It is embarrassing to suggest you were abducted by aliens. This same standard should be applied to gods of all shapes and sizes. The more a religion is ridiculed, the less will their believers be willing to humiliate themselves.
Once-Proud Canadian, Enlightened Atheist, Gaming God.