Actually, I do strongly feel that non-consensual circumcision should be dictated, much like how it is dictated you won't starve or beat your kids. Or like how you have to put them in a car seat. Or get them medical care, regardless of religious beliefs in some places. Like it or not, there already is a lot of parenting that is dictated to parents with mandatory "dos and do nots." Non-consensual body modifications really do need to be a "do not."
Yet the differences are clear. The instances where we stop parents from engaging in behavior are instances where actual abuse occurs or a parent is negligent in their duty.
So far you have offered that circumcision is not necessary. OK but we don't say someone can't do something because it is not necessary.
You suggest that the parents can achieve the benefits a different way. OK but that doesn't mean they are negligent or abusive because they choose a different way than you would.
You say that the parents choice is permanent. Ok, but parents make choices all of the time with permanent repercussions.
It is not abuse. It is not negligent. That it is different than you would choose or want for the child is not enough. Lots of people believe choices parents make are wrong. That doesn't mean they get to tell the parents they cannot choose that.
I understand you believe permanent body modifications cross a line. But we allow those when we cannot show that there is harm without benefit, or harm such that a reasonable person would not choose the harm for the benefit.
Reasonable people can choose circumcision. It is really that simple. A large numver of medical professionals agree with this. That you don't is ok. But realize that it is your belief. Realize that saying it is unreasonable is more than just saying it is unnecessary. And, realize that you are saying all of those medical professionals, who think it is a reasonable choice for parents to make, are wrong.
To say that you should be able to dictate whether another is allowed to do something is more than saying they should or should not do something. It is a pretty extreme position you are taking.