In 100 years, I could imagine a society where young people are expected to find a gender identity in the same way as they find other aspects of themselves, and maybe their gender identity changes a few times over their lives.
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Especially in people younger than ~20, I think that transgenderism today is often (but not always) a result of depression.
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Many young children dream of being an astronaut, a firefighter, or a police officer when they grow up because society views them as heroes of the world. It is also not uncommon for young girls to go through a "tomboy" phase or a young boy to go through a feminine phase. Both are totally natural, however, most people ultimately outgrow these types of phases.
Just as it would be a bad idea to send a six-year-old into space, it it bad to chemically castrate a young teenager. It is even worse to pressure a young child into thinking they want to be a different gender, and to put the child through surgery in order to "affirm" what the preditor is saying the child's gender is.
In general, I don't have an issue if someone wants to falsely claim they are a different gender than they actually are. What I do have a problem with is that person imposing their nonsense on other people, as well as using their fiction to remove rights and privacy from others.