I see nothing wrong with it as long as it's done by a qualified professional. I wouldn't let anyone near me or anyone I loved with a piercing gun. They don't sterilize those things and they're little bacteria breeding factories.

It's very traditional in some cultures and if it's done when the baby is young enough they don't mess with them while they're healing.

Here's my story:
I begged and begged and begged my mom to let me get my ears pierced. When I was 8 she finally relented and took me in. I always heard that they used a "gun" but I didn't know anything about it. My older brother was with me and told me they stood you up against a wall and shot you with the "gun" and somtimes they missed! LOL He was such a butt head! I freaked out and wouldn't let them near me with the gun for fear I was going to get shot. Hehe. I let them do it about a year later.