We're getting pretty far afield from the teaching of science here. But if you must know my personal opinion, it's that legal documents should allow for exceptions from the norm to be noted where applicable. I would not support the right for a person to select their legal classification arbitrarily though, it should be based on objective biological conditions, such as hermaphroditism.
I think the commenter you’re responding to is pointing out that there should be options for rare exceptions, but for most other people, they’re not committing fraud by marking one option or another, because they can simply change that answer tomorrow. I feel like a boy today, so I marked it on my passport. I am a girl tomorrow, so I change my answer.
