This is my opinion, and I share it in the interest of open discussion. I have a great deal of respect for the writer.

A lot hinges on whether one believes sex and gender are objectively real. If these qualities are real, then they have definite bounds, limits, although we may not know what those bounds are. Our understanding of these qualities is dependent on many things; and there is always more to be learned. We cannot be dogmatic.

Nevertheless, personally, I subscribe to the gender binary. I believe that sex and gender are objectively real qualities, and it seems clear to me that human beings are designed to be male or female. It's a matter of continuity of the species. It is inefficient for gender and sex to diverge. Gender dysphoria is not a survival trait.

Non-binary and "gender fluid" make no sense to me. Perhaps they're real, perhaps they're not. I have encountered several trans women who have said that they previously identified as non-binary; this suggests to me that "non-binary" may simply mean that one hasn't figured out yet on which side of the divide they belong.

Does this mean people shouldn't be free to identify as non-binary or gender fluid? Of course not. We're all on a journey of self-discovery; and, if it helps you to identify as non-binary or gender fluid, then more power to you. The fact that I don't believe in these things doesn't matter; and, in any case, I could be wrong. I support you on your journey. If you require my belief, however, that is unreasonable.

I make this comment only because this point of view is never expressed within the trans community. It is important that we embrace reason, and respect differences of opinion. If we can't do that with each other, we will never be able to do it with the cis population.