You could play your priest as a sort of Social/Monster Darwinist.
You believe that Lamashtu has called you to cull the weak so that the strong and mutated survive and flourish. You can view killing a monster as returning it to Lamashtu so that she can make use of it and give birth to something better.
In social settings, you would find most humans unsuited for world Lamashtu is building, but you would think that those strong enough to adapt and survive are blessed by Lamashtu (even if they don't know it). You have no sympathy or pity for the weak, only respect for the strong.
You could also be a heretic in that you think of abnormality as a "deformity." You would think of anything that sets you above "normal" as a gift from Lamashtu, even if it is something non-worshipers of Lamashtu might also value. (i.e. abnormally high strength, abnormally high con, abnormally good swordsmen)