We have a son and we chose not to do it. Our reasoning was pretty straightforward - it's not my penis...it's not my husbands penis....so we don't feel that the decision to alter it permanently in such a way is ours to make.
A few other reasons - we would never even have considered it if he was a girl so could not justify doing it to a boy, and once his foreskin is gone it's gone - if he grew up to feel that he never wanted this procedure done it is irreversible. And we did not see any compelling medical evidence that there is any benefit to it.
But the main reason by far was simply an issue of his personal autonomy - his penis, his choice.