After reading previous BB entries I think I have this right:
If a neutral aligned character initiates combat against an evil NPC, their alignment drifts in a certain direction.
If that same neutral character just "happens" to "accidentally" wander into an area known for evil NPC's to attack a player on sight, and the player lets the NPC initiate combat, then there is no alignment drift?
Hmmmmmmmmmnn, looks like Ol' Kaga has found another "tax shelter".
I don't see a problem. Self-defense is different from a conscious attempt to harm someone, and while some might call wandering into a mafia club and opening fire Evil, pretty much no-one would call it evil to fight off a mugger in that same club. What's the big deal?