1. Circumcision does not maim, which is to say, it does not destroy the function of an organ. The penis will still have perfect functionality; some claim there is a bit of impaired sensiivity, but others say that is compensated for by improved longer-lasting erectile function; so it's not like an amputation and more like (by way of analogy) a decorative body piercing
2. Circumcision can be additionally justified by an objective therapeutic advantage, in that a circumcised penis is provably less likely to transmit a range of STD's.
This holds true just for normal male foreskin cicumcisions, by the way; it does not apply to something radically different, which is female "circumcision" ---actually genital mutilation --- which dangerously impairs the healthy function of the sexual/reproductive structures involved.
Thank you for the common sense explanation.