My cousin had this on both hands when he was born. They were both removed before he was born.
Now, I realize this is rare and considered a disorder, but if its not actually causing a problem for the child, why shouldn't it be his/her decision to remove the extra digit(s)?
I believe in either this case or the with circumcision, it is the parents choice. As far as having female circumcisions (of any kind), if there was research to show that it could help avoid future problems and did not harm the girl (beyond the little bit of pain), then that too should be left up to her parents. Most female circumcisions though are seen as more harmful and traumatic (since most of the ones people hear about are not performed on baby girls but rather toddlers and older girls, and are not normally done by a professional doctor). This would probably scare most parents into opting not to circumcise their daughter even if there were/are benefits.
Removing the foreskin is no more mutilation than piercing ears of an infant. Some piercings are temporary, but many are permanent. I have known plenty of girls who had their ears pierced as babies and they didn't have to wear earrings for their holes to stay open. (I always wished I was like this, because mine grew up twice within about 4 or 5 years.) My mom's and sisters' have both had theirs stay open since they were done more than 10 years ago, and they rarely wear earrings.q