I would recommend starting with the blatantly obvious. For example, it is "right" that stabbing yourself will cause you to die horribly. If someone decides that it is "right for them" that stabbing themselves would instead result in them winning the lottery, they will make a very bad decision.

Also, your examples for how belief in heaven could hurt you aren't the most common ones. I'd list things like abortion, fornication, drug use, and any other issues theists and atheists tend to disagree on. Even if your decision only effects you, it's still important, as with the stabbing yourself example.