Bill, there is more than one way to spread God's word. And a LOT of them are much more effective than knocking on doors.
When someone comes into my shop and asks what brought me here, I say "God." That will usually open a conversation, and without making them feel like I am invading their privacy. Just read the responses on this thread. NOBODY likes having strangers knock on their door and tell them they are d a m n e d. But no one takes offense if I tell them about MY life, and MY experiences with my Lord. That is called planting a seed, and I would be willing to bet that seeds planted that way take root and grow much more often than seeds planted at a stranger's door.