But if a trans woman is a woman, why put the prefix trans in front of woman? If they’re one and the same, why bar cisgender from playing transgender roles in film because “casting cis people in the roles of trans people is so harmful“?

Because they want to have their cake and eat it too; transgenders demand simultaneously that a.) society acknowledge their status as full women, indistinguishable from actual women and b.) society celebrate their special uniqueness.

Schizophrenically, while reserving trans roles for trans actors is the stated objective because “representation matters,” it is also “typecasting” to cast trans actors in trans roles because they’re not a monolith.

They’re all unique (and stunning and brave) individuals, but they’re also all members of a highly protected social class that deserves privilege based on gender identity.

You can’t win, by design, no matter how hard you strain your patience to accommodate them. In the end, even the most devoted ally can be accused of transphobia when it becomes convenient.