What about all the people who think they have free will?
Here's something fun: Can you actually believe that you don't have free will? I don't mean some silly statement like "I can't see how free will is possible", but actually observe yourself acting, free from the illusion? After all, with other illusions, you can "shake them off" an see them for what they are -- separating what is from what is apparent. If you can deny such a strong and ever-present aspect of your own experience, how does that affect your perception of yourself? Can you take pride in your accomplishments or feel shame for your failures? Does it have any meaning to you to know that the meat robot you happen to inhabit made, for example, a +5 post? It wouldn't be the meaningful, experiential, you, after all, that accomplished that, but some 'other' external to you. You were just along for the ride. Is that consequence a fact you recognize or do you hold on to the illusion?
Or the ones who can look straight at a penis vs. a vagina then declare that gender is "socially constructed?"
There's a distinction they draw between sex and gender. You're having trouble understanding their position because you conflate the two.