If ear peircing involved removing the whole entire earlobe or external ear with the same method of painblock used for a circ, only then would I be willing to draw a comparison.
If I had a little girl, I'd let her decide to get her ears peirced when she was at an age old enough to understand the procedure. I was six when I got my ears peirced. I was not old enough to take care of them myself, my sister took care of my ears religiously until they healed up. I don't regret for a minute decided to have my ears peirced when I was six. I knew it would hurt, and I didn't cry. And they were my ears.
If my kid wants to get circ'ed before he's an adult "just because", I'd say no. (Unless there are extreme medical issues...) He needs to be old enough to understand what a life time without a foreskin will mean, what nerves would be removed/damaged, and he needs to be able to fully understand how this will effect his sex life as an adult and be ok with it. I think he'll only be able to grasp that as an adult or close to or over 18. If he's, say, 11 or 12 and he wants it done, I don't think he could really grasp the whole scope of such a decision to amputate an important sexual functioning part of his body, so I'd say no.
It's totally different from ear peircing, I'd say.