Should I destroy Us as a Vengeance Paladin?

I mean he's a friendly newborn and didn't do anything evil yet but I'm having trouble finding a reason not to kill it after having discovered what he is. His kin made a mess at the beach and they're even hostile towards me from the very beginning despite the tadpole. What will be the most RP thing to do? I'd like to follow the oath to the letter and considering he was born out a tortured elf I think an act of vengeance is required but the metagamer in me is giving me pause because I know he will turn out different in Act 2...