Should Christian Groups Evangelise Outside JW Conventions?

Jehovah's Witness District Conventions - Is it right for Christian groups to take this opportunity to stand outside these events and witness to the witnesses? They come to the doors of Christians trying to win them over out of thier churches and into the Watchtower religion. Shouldn't Christians, therefore, take this opportunity to go to where many JWs congregate to win them out of the Watchtower and into Christ? Is it a waste of time? Does it bear fruit? How do you witness to someone who thinks you are already "an agent of of Satan"?


Above video: JWs in Manchester city centre during District Convention dinner break.