Corrected entry: Leo tells the sisters that the darklighter gets his victims to commit suicide because it's the only way to prevent a future whitelighter from becoming a whightlighter. But in future episodes with darklighters, he tells the sisters that if the darklight kills their target, it will prevent them from doing all the good they are destined to do as a whitelighter.
Corrected entry: Phoebe has to explain to Leo that she and Prue were once in a car accident and Phoebe was injured badly, but if Leo has been watching the charmed ones since they were children or birth, wouldn't he already know about it.
Correction: Maggie had already done all the good she was destined to, meaning if the Darklighter was to shoot her, she would still become a whitelighter because she had already earned her wing, as they say. It's believed that the only sin that cannot be repented is suicide, so it would be the only way to damn her.