> Whether someone is a male or a female is simply a question of biological definitions of observed reality, just as whether an animal is a dog or a cat is simply a question of biological definitions and observed reality. A man who thinks he is a woman is simply mistaken by definition, just as a man who thinks he is a dog or a cat is mistaken by definition.

Hard disagree. Even with a strictly genetic interpretation there are more than just two sex-chromosomal configurations, but leaving that aside there are many of us who believe that gender, unlike biological sex, is a social construct. Saying "you must be a man because you were born XY" is roughly equivalent to saying "you must stay home and cook dinner because you were born XX".

Let's say we had the ability to genetically re-engineer people into whichever sex they wanted. Would you still be opposed to letting them do so because they were born a different sex? Would you deny genetic treatment of debilitating diseases because people were born with them?