Hmm, "delusional" is a bit underspecified.
How about "There's no solid evidence for a gender bit in the brain. While many or most transgender people feel something, explaining that feeling as "I'm an X brain trapped in a non-X body" is essentially a memetic phenomenon. Additionally, genderqueer and non-binary persons are typically participants in a memetic fad."
I think that's what I believe; summarizing this as "trans people are delusional" seems harsh and uncharitable to me, but I can see how someone might say that's exactly what it is. If you think now that the above is obviously wrong, I'm very interested in arguments/evidence.
Humans are made of both biological and memetic (social) stuff, though. It's famously difficult to ascribe any particular behavior to just one or the other -- the old nature/nurture debate being one aspect of that -- but even if you could, you can't necessarily describe one side of that as more "real" than the other side -- I am both my flesh and its neural activation patterns. One reason I believe most transgender people describe a purely physical (brain) basis is that using the language of desire is severely socially proscribed: it's not viewe...
What is something you used to believe, preferably something concrete with direct or implied predictions, that you now know was dead wrong. Was your belief rational given what you knew and could know back then, or was it irrational, and why?
Edit: I feel like some of these are getting a bit glib and political. Please try to explain what false assumptions or biases were underlying your beliefs - be introspective - this is LW after all.