Of course, the phrasing _If gender dysphoria is caused by ..._ implies that we're considering _gender dysphoria_ as one category to reason about homogenously. But different people might want to transition for very different underlying psychological reasons. What categories we use may not be a question of simple fact that we can get wrong, but if, empirically, there happens to be a sufficiently robust statistical structure to the simple facts of the cases—if some people want to transition for reason _A_ and tend to have traits _W_ and _X_, but others want to transition for reason _B_ and have traits _Y_ and _Z_—then aspiring epistemic rationalists may find it useful to distinguish multiple, distinct psychological conditions that both happen to cause gender dysphoria as a symptom.
Analogously, in medicine, many different pathogens can cause the same symptoms (_e.g._, coughing and sneezing), but doctors care about distinguishing different illnesses by etiology, not just symptoms, because distinct physical mechanisms give rise to distinct treatment decisions, either immediately (_e.g._, a bacterial illness will respond to antibiotics, but a viral one won't) or in principle (_e.g._, today's treatments might be equally effective against two different species of bacteria, but future drugs might work better on one or the other).
Of course, the phrasing _If gender dysphoria is caused by ..._ implies that we're considering _gender dysphoria_ as one category to reason about homogenously. But different people might want to transition for very different underlying psychological reasons. What categories we use may not be a question of simple fact that we can get wrong, but if, empirically, there happens to be a sufficiently robust statistical structure to the simple facts of the cases—if some people want to transition for reason _A_ and tend to have traits _W_ and _X_, but others want to transition for reason _B_ and have traits _Y_ and _Z_—then aspiring epistemic rationalists may find it useful to distinguish multiple, distinct psychological conditions that both happen to cause gender dysphoria as a symptom.
Analogously, in medicine, many different pathogens can cause the same symptoms (_e.g._, coughing and sneezing), but doctors care about distinguishing different illnesses by etiology, not just symptoms, because distinct physical mechanisms give rise to distinct treatment decisions, either immediately (_e.g._, a bacterial illness will respond to antibiotics, but a viral one won't) or in principle (_e.g._, today's treatments might be equally effective against two different species of bacteria, but future drugs might work better on one or the other).