My philosophy on tricky moral choices is that the more informed the players are, the more powerful and interesting the choice is. So give stuff away. Spill secrets. Maybe not the whole thing, but don't try to be subtle. Give more information than you think is necessary for them to "get it", because your current level of information didn't work out. You want players to get to the good part, so don't bury it deep and expect them to dig. Start them with something solid that provokes curiosity.