Okay so first you say "circumcision does not offer any benefit to boys or girls", and then in the same sentence you say "but for boys it is a little beneficial". Circumcision does not protect from infections. I can make the case that it actually increases vulnerability to infections! In any case, if we are going to circumcise boys because we think it offers some protection against UTIs and STDs then why not circumcise our girls as well? After all if the penis is so easily infected then what about the vagina?!
Circumcision, by definition, creates a difference in penis size as it is an amputation of part of the penis (and a very significant part at that!). And circumcision, again by definition, does involve cutting the foreskin.