I want to thank all those contributing to this discussion. It's been far more interesting and educational than I'd imagined when I asked the original question. It's been very thought provoking.
I believe understand why those mothers (I think they were all mothers) felt it was right to have their daughters' ears pierced at such a young age, and believe me, I am not criticizing. Whether I believe it's right or wrong is immaterial: they are your children, and your responsibility.
For my part, I would have to join with those who feel that it's something which should wait until the child is old enough to make her (or his) own decision, after being told all the pro's and con's of the matter. I don't have any daughters, so I'm speculating, but I might even go so far as to require my daughter to pay for the procedure herself, with the idea that if she is not mature enough to save the money required, she's probably not mature enough to make the decision.
The same would apply, of course, to tattoos. I don't have any and I don't particularly care for them. Like tydnchaynz, I think they should wait until they are 18, or at least old enough to hold a part time job. My two boys are both over 21 and out on their own and, to the best of my knowledge, do not have any tattoos or piercings. I seem to recall (my memory is quite fickle at this age) that one of them once asked about getting a tattoo, and his mother and I both decided that he should wait until he was older. The subject never came up again.
When the subject of circumcision arose I was caught off guard. I never would have related the two subjects. But in this case, as I stated earlier, it's a medical procedure, done by a doctor in a hospital, for a valid medical reason. As parents we have the right to decline such a procedure if we wish. It's certainly not life-threatening if the child is not circumcised, though there can be medical complications down the road, as stripedangel noted. I don't believe you can equate this with a purely cosmetic procedure such as ear piercing, especially when performed by a non-medical person in a mall kiosk!
Thanks again, everyone, for your comments.