I don't put much stock in people who tell others how they're going to hell for this, this, this, and this, but that's all they do. I've known plenty like that, and whether they're right or wrong, the Bible tells Christians to "speak the truth in love" (Ephesians 4:15) and to be careful how they judge others (Matthew 7:2).
Debating them is usually ineffectual, as they take any challenge as a sort of persecution and, thus, as a sign that they're doing good by God.
Besides, you don't know enough about the topic to put a dent in them, anyway.