We never know what we don't know. If someone wants to talk, listen.
Cult-think mentality easily fills our fears with mental constipation: "They want to sell you snake oil," it says. "Don't let him speak. He will cast a spell on all who hear!"
Cult-think never solves problems. If someone wants to talk, listen. There is no good reason not to listen.
They may want to warn, defect, apologize, or even attack again. But, it doesn't matter how evil they are or have proven to always ever be. If someone wants to talk, listen for one reason: You're not telepathic.