Unlike most people, I find engaging missionaries on the street (or sidewalk) a productive and enriching activity. When I see two guys in suits wearing nametags trying to start conversations with people, I'll go up to them if I have the time. I feel obligated by my own worldview to challenge them in their beliefs so that they might grow and be better practitioners of their beliefs. I try to give them insight into a worldview that is completely foriegn to them, and hopefully it will result in the missionary having more empathy and understanding of a view of reality that they would otherwise not have.
I use two methods of talking about religion and worldview (I find the term "worldview" a better term, since it encompasses both religion and secular belief systems). The first is to discuss the phenomenological aspects of experience, especially religious experiences. Most religious people have had experiences that caused them to convert to their religious belief, or confirm a pre-existing religious belief. Similarly, most humanists, atheists, or other practitioners of secular worldviews (not to be confused with people who don't have an explicit worldview) have analogous experiences. The key point is that while the experience can be explained, there are aspects of that experience that cannot be conveyed to another person. My experiences that caused me to adopt a humanistic view of reality cannot have the same impact when described to another person.
The second thing I do is to respond to a request with an analogous request. For example, if I am asked to read the Bible or Book of Mormon and make up my mind about it, I will ask them to read Dawkins' The God Delusion, or Dennett's Breaking The Spell, and contemplate whether that is a more rational approach to belief. If they ask me to try to talk to God or pray for some divine revelation, I will ask them to try to look at some of the secular worldviews, and try to understand how those explain belief in God.
The goal in both of these is to avoid the standard rote arguments that have been rehashed for endless years, and to try to create a non-threatening way of engaging and challenging those who are trying to proselytize. In my experience, most every missionary I have used this on has enjoyed the conversation, and I feel that it has helped both parties get a better understanding of the other's worldview.
I will note this method is not good for the showy street preachers who preach hellfire and damnation on streetcorners. Those people aren't interested in rational discussion, rather they are using theatrics to try to provoke a response.
I would appreciate if anyone who has any other ideas for challenging missionaries in a non-advesarial way would post them in the comments.
In my next post, I'll talk about the psychological mechanisms underlying a "crisis of faith" and how it relates to conversion and growth in a persons world view.