Comment by lliamander

My point is that the idea that there is this (clear) distinction between sex and gender is not universally accepted and that there may be some reasons why people are skeptical of it.

In terms of the science of sex differences, my understanding is that they (at least sometimes) don't make the distinction between sex and gender because many traits and social behaviors that we might assume to be part of "gender" end up having a underlying biological component as well (that isn't easily separable).

In terms of the general populace, I would say that for many people the realities of their biological sex (including their reproductive capacity) have a great deal of impact on their gendered experience.

This is not to say that the experience of trans people should be ignored. But this may help account for some of the surprise people express at statements like "trans women are women" or "women is not a sex".