Fear tactics seem to work for other religion, why can't it work for Buddhism?
One of my friend told me this before about her husband and how she appreciated that her husband was god-fearing hence he is a good man. To the spiritual ones or if they are already Buddhist, etc, I feel that karma should be explained. What is the point of calling yourself a Buddhist and not believe in karma?
For non-believers, I wouldn't go so deep into karma and the three lower realms, etc. I would focus on what goes around comes around. It is quite normal for people to believe that there is consequences to all their actions. Give simple scenarios that makes sense in the layman term such as if you drink water, your thirst will be quenched. If you hit or scold a stranger, you will get shit look, scolded back or beaten. It's samples of action and reaction. When people understand that karma is not something mystical but it's something that makes sense in the ordinary world, then you can explain further about why some are born unfortunate, disabled and in a bad condition. Make them think by asking questions.
Hope this help.
