It seems to me that choice should be between the child, their family, and their doctors.
Disagree?
I'm agnostic. For now, I'm provisionally taking the null hypothesis for your claim: It should not be a choice between the child, their family, and their doctors.
Can you tell me more about your guiding principles, when and why you make exceptions, etc.?
For example, there are many things that we (as a society) say should *not* be a child's choice. There are two broad sets of guiding principles for this, both with exceptions.
One set of guiding principles is along the lines of, nothing should be a child's choice. And then we make exceptions in some cases, where we allow the child to choose.
The other set of guiding principles is along the lines of, everything should be the child's choice. And then we make exceptions in some cases, where we don't allow the child to choose.
So. Your idea that a child should be allowed to choose their gender, pre-puberty. Does it fall under your guiding principle that children should be allowed to make their own choices, and you can't see a reason to make an exception here? Or is the other way around?
If that's too broad a consideration, we can keep it in the realm of medical choices. It's not hard to find a kid that doesn't want to be jabbed with a needle. Do we let them choose for themselves whether to get vaccinated?
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It's a similar case with doctors. There are plenty of medical procedures that we don't leave to the doctor's discretion. Late-term abortions of convenience, for example. Euthanasia, for another. Should this procedure be one of them? Why or why not?
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If you think that as a matter of social policy we should let it be a choice between the child, their family, and their doctors, then it's incumbent upon you to advocate for this policy. Before you seek agreement or disagreement, you should explain why you think this is a good policy. What principles are you basing it on? How does it follow from those prinicples? Is it an exception to a general rule, or an application of that rule? Are you prepared to address the concerns and objections raised by others, based on the same reasoning? Etc.