The only way you have a chance is if you understand where they're coming from. Then you can chase them away just like they were Mormons or Jehovah's Witness missionaries.
Off to bed...sorry to leave but thx for the repartee.
Actually door to door missionaries of any sort amuse me. I go out on my doorstep and preach Orthodox Christianity to them, sending them away bewildered. (I've toyed with the idea of keeping a tract or two handy, but the come so seldom. . .)