Anorexia and other body dysmorphia conditions are reasonable comparisons.
Yes there are differences: Anorexia is life threatening and to support it may lead to death so you wouldn't. But to treat it you do need truth and honesty,you do not lie, and the aim is to make them comfortable with their body instead of destroying it through starvation.
A better comparison is probabky other extreme body modification through surgery. If someone is seeking to look like a cat, or Barbie, or a vampire, or even just a never ending an obsession with altering their perfectly normal body, is this something that should be supported in children? Even if its causing them distress to not be this thing they want, even if puberty will make it harder? NO.You don't harm healthy developing bodies for an irrational dysphoria.
That should be obvious.
Adults can do crazy extreme things to their bodies. But even then I don't think doctors should support it, it shouldn't be regarded as health care, and it shouldn't be viewed as the answer to a mental health problem.
But with children it should obviously just be seen as insane and evil to consider it.