You’re right that everyone is always in this epistemological bind: Either we have to claim perfect certainty (which is implausible and arrogant) or else we have some uncertainty (in which case, on what basis do we challenge each other’s self-knowledge or try to limit others from living their best life)? Thing is, the transphobes have already rhetorically hacked this, and they exploit it. They portray themselves as “conservative” about avoiding action on uncertainties (e.g., they advise people not to take hormones) and as guardians of the status quo (e.g., they want to prevent people from taking hormones). They claim to be “certain” of their “uncertainty” about trans people. Of course their position reveals itself as hypocritical when it’s phrased that way. A good philosopher would hammer at it. But they aren’t philosophers and neither is their audience. They don’t care. If “Just asking questions!” is turned around back at them, they won’t give a real answer. They’ll just get louder.