Blarg.
Calenthang's past was a dark one, right.
Dark elves and demons and the like. Calenthang hates dark elves. Hates them enough for them to drive him evil with his passion to eradicate them from Faerun.
Genocide, in my mind, is something to consider Evil.
Just Lawful Evil, mind you. And really, it should only come forth when concerning drow.
I'm making sure to adjust his personality here and there to make it so it's not such a big change when it finally happens. That shows in his thoughts (and his fighting actions).
A sort of build-up to the ultimate alignment shift.