I really like Inid's recommendation on bringing up the reality of hell. The same with Mormons, you can bring that up with them also to help them see the inconsistent teachings within there church and at the same time minister to them as an unbeleiver.
Hypothetically, if I was Satan I'd make religions that tried to keep up Christian external morality and convince people that the realities of hell don't exist. It's a winning combination to feel like a "good person" and feel as though you are pushing a very "tolerant" & "peaceable" religious view. Very deceptive and very effective... Satan does truly come as an angel of light to decieve.