Defilers? That's easy. Just let them pass any strain incurred on to the plants around them. The more stat losses they would suffer, the bigger the circle of defiling.
Easy power? Check. "Better" than Preservers? Check. Immoral? Double check.
Very nice mechanic. Come to think at it I think I will make a version of it with an evil wizard (TM) in my game; with dark magic he let's his peasants take his strain damage so that he can use extremely powerful magic ~~
