I've got to wonder whether what they get from this door-chugging approach. If I met someone in some other situation, say a party or even a bike ride (a bike ride!), and discovered they were a JW (or Mormon or somesuch) I might well ask them about this. What are the core beliefs of JWs, how does this get expressed in their daily life, what do their services and rites look like, does their church have an opinion on x, y and z...? Conversion is highly unlikely but understanding is more probable. Whereas knocking on the door is just going to annoy most people.