You're doing several flawed analogies there. A foreskin is not like hair or fingernails, because the last two grow back. The procedure isn't fail-safe; it has the potential to go wrong, and when it does...
Also, hare lips, and especially heart defects, are more, way more, life threatening than some foreskin; and the social stigma associated with the first one should not be overlooked. To be fair, I've heard there are women in the US who don't like circumcised penis, and that *could* be a valid reason for an adult man who cares about such matters, but then again, that's something a baby shouldn't worry about.
You mention smegma, cancer, and STD's as your reasons for circumcision. The first one is solved with basic hygiene, and for the later, proper use of condoms is much more effective at STD prevention than circumcision. On HIV: circumcision's effectiveness is of about 61%; it would be roughly like letting my fate be decided by the flip of a coin. It's virtually impossible for a condom to allow HIV transmission as long as it is properly used. I could not find the source on the cancer claim.
Anyway, sex and cancer are not part of children's worries. Let them grow up and then decide what do they want to do with their bodies.
I can also make a similarly flawed analogy. What if we cut all women's breasts off? Breast cancer would cease to exist, and maybe men would be less driven to have sex with them, which would lower the chances of catching an STD. Sounds ridiculous doesn't it? (to be fair, masectomy is sometimes done preventively in women whose genotipe make them very likely to develop breast cancer. That's not the case with most women though, and those who go under that procedure do it under their own free will)
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To build may have to be the slow and laborious task of years. To destroy can be the thoughtless act of a single day. - Winston Churchill