Those that get it done for medical reasons being called mutilation would be offensive.

Right, because they weren't mutilated, they had to have a procedure done for a medical reason.

Any non-medically necessary surgery to a child's genitals is mutilation. They have no way to consent, and anything short of a medical necessity is the parent making massive changes to their child's life based on their preferences. To make the point crystal clear:

• If I have a kid and the arm ends up gangrenous, we would remove it as it would be medically necessary for the child's well-being
• If I have a kid and think it's cool to have one arm, I would be trying to mutilate my child by removing it for no reason

How is performing a medically unnecessary surgery on a child's genitals not mutilation? Again, you're changing their body surgically without their consent for no reason aside from ignorant beliefs.