How would you respond to the following quote?

"It is now evident that humans cannot be characterized as a member of 1 of 2 clearly defined units: male or female."

The quote is of course from this journal article, which argues that variation in anatomy, gender identity, and sexual behavior indicates we cannot reliably categorize individuals as males or females. https://journals.sagepub.com/doi/full/10.1177/2470289718803639

But it does not follow that variation and overlap between two populations means the two categories cannot be reliably defined, nor that they are socially constructed.

Variation in anatomy, identity, and behavior does not make more than two sexes.

This article is one of many that utilizes the diversity of sex differences to argue that sex is not binary. But of course, this is an easy strawman: when you ignore what sex is at the ultimate level, you can claim any variation of sex-related traits disproves a binary.

But no one ever claims that people's physiology/anatomy, identity, and behavior fits into two neat boxes. There's considerable variation and overlap.

(When it comes to reproductive anatomy, these structures fit 'unambiguously' into one of two distinct forms >99.98% of the time.)