You're still not seeing. You have your own ideology.
And poststructuralism does not say "we don't exist". It says our reality is subjective. It throws out any idea of authenticity. And I likely prefer this ideology because it makes the most sense to me, just as you prefer your ideology because it makes the most sense to you. Rene descartes has been widely criticised - I imagine you know that. Poststructuralism is also criticised - possibly by those that would prefer to follow Marx or Descartes. But this really is about preference. Poststructuralism isn't about us not being able to prove we exist, either. It by no means throws out physical evidence. It may say "gender is performance" but it does not say "gender is not real" - because gender is real. What's not real is some of the traditions we relate to gender (though this is a minefield and debatable) and what is certainly not true is that gender is binary - one or the other.
Oddly, we're actually coming from the same place on this one. I base my ideology on what I perceive to be empirical evidence. The fact that if a person is on the spectrum of hermophroditism (and this is a wide spectrum that does not only include what organs you have but what hormonal balance you have) then it is not possible to say whether they are female or male, shows that the idea gender is binary is impossible. That does not mean we should not use words like female or male - how could we live like that? - it simply means we should remain within the understanding that neither exists in a concrete manner. They exist, of course, but spectrally. Poststructuralism is a school of thought that sees the world as a chaotic spectrum on to which consciousness draws arbitrary lines in order to understand this. There is plenty, plenty, plenty of empirical evidence to show this is true. The part you are questioning, I imagine, is that this has consequences. But when you think about it - how can it not?
But this is getting into a silly battle of the philosophies

We'd never agree on this point. I'm not sure why you want to change other people's ideologies but if there is good reason then it is as @
Sonya said - manipulation, people skills. But no one is ever going to throw out their reality. It is how they grasp the world.
And when it comes to relevance to this thread - this thread is precisely about this isn't it? Altering the way people see the world to conform to your reasoning? I see the world differently