So, I got the idea reading the BoED and Races of Eberron. Vow of Peace still lets you inflict lethal damage on constructs, and warforged paladins can smite constructs as if they were evil.
Basically, he's a member of the Crucible (from Faiths of Eberron, I think) - the guy is convinced that his race are too dangerous as weapons to be allowed to exist.
LG Dragonborn (mind) Saint Warforged paladin 3/ranger 1/warforged juggernaut 5/???
Feats: Adamantine Body, Nimbus of Light, Sacred Vow, Vow of Peace, Vow of Poverty