Align in fl means if you are evil, you are evil. A paladin, esp if he follows purity - should - attack any evils. Their god tells them they are evil and you can rely on gods.
If it is an outcast wannabe, this drow should rp that way and also apply for it (we've had that before) as well as talk to the paladin in question.
This still does not mean that a purity follower has to go out of his way to attack ranking parties or kill a rank 45 5 times in a row. Getting someone to quit can't be the goal if you want to have fun pking them again in the future.
