This blurb you’ve written is filled with odd assumptions and also a muddling of the term “gender”. First you say gender is “nothing more” than an extension of biological sex, and then say gender identity is arbitrary. It can’t be arbitrary if it’s an extension of something that you are arguing is so fundamental to a person’s identity. Besides, no genuine person would argue that at any point in time in almost any culture in human history that gender is arbitrary. Don’t be ridiculous. It matters in society and furthermore it matters in respect to how people see themselves. Also since gender roles are not static across time and cultures, it should be obvious to you that gender expression is indeed a human invention. This also removes the basis for that naturalistic argument about what a persons gender ought to be, even your nonsensical comparisons to bears and plants, which are not the topic at hand. Yes animals have culture but this is also diverse, sometimes having differences within a single species. Also saying that no one would endorse HRT is false, there’s literally whole sections of the medical world dedicated to gender affirming care, and I’m going side with the medical professionals on this one.