If you can't explain what bad is, then I am unable to discuss this with you

Bad is causing harm to people who don't deserve it. Convincing someone in the existence of hell is harmful - you are theatening them with the worst thing possible, convincing someone of a lie to compel them to serve the chruch through donations of time or money is harmful, convincing someone that they are innately sinful is harmful psychologically, convincing someone that morality is tied to religious institution is harmful. Children are least deserving of harm and so harming them is bad.