Lexi, thanks for looking into this. It sounds like the hypospadia angle is weak. But I am curious what you think of the following.
I should have pointed you in the direction of what convinced me this is a hidden public health emergency. It's the work of Dr. Shanna Swann, who wrote the book on the collapse of sperm counts Count Down. Additionally, she has done lots of research to show links between pollutants and endocrine effects.
The alarming result: mothers exposed to greater levels pf phthalate pollutants (released by lots of things but especially plastics) had male children with lower anogenital distance, which then correlated to gender atypical play.
I think it makes intuitive sense that a global sperm count collapse of 50% could be related to a greater prevalence of people who experience gender dysphoria. Pollutants that alter hormonal functioning could be the common thread.
On a separate note: The analogy to left-handedness is suspect for evolutionary reasons. While right or left-handedness has no known link to reproduction, certainly a high population which experiences challenges to reproduction effectiveness would not be selected. So it is actually extremely counter-intuitive that there should be a sizable population that experiences these issues at all. I think it makes much more sense to look at what has changed in our actual chemical environment than to layer the cause exclusively in culture.
This is the troubling implication: while the acceptance dynamic would expect the trans population to reach a stable "real" percentage like left-handedness, if the chemical theory is true the theoretical max is the full population with sufficient dosage of culprit chemicals. Over the decades where the rate is significantly increasing, insufficient attention to the chemical theory could serve as an enabling factor which extends the public-health crisis. At some point, the results would be clear -- but I think it is worthwhile to consider this option as early as possible, as the impacts are global and population-wide.
That's why the imperative on scientists interested in these issues should be to definitively prove that the chemical theory is impossible. Swann's research convinced me that it is highly plausible and I hope you can find reasons to strongly doubt that.
