No no, what you do is you ask them if they know why the church is making them go door to door. When they say "to spread the word of God" you correct them. "No, they know that going door to door won't get new members of your church because doing so is rude. They want people to get mad at you and treat you poorly so that you run back to your church saying how mean everyone was. That's when they pull YOU in closer. You're being played." It won't save their souls from the cult, but it plants a seed of doubt. And if they go back and tell the church what you said, you'll be put on a list of houses to not return to.