Because we are already struggling to be accepted in society and every time a big actor plays a role in a big movie like this where they portray someone who doesn't conform to normal gender roles, they make the person out to be totally vapid, arbitrary, and generally ignorant of everything transgender people are supposed to be educated about, everything a real transgender person is educated about.

I understand one point of comedy is to make people laugh at issues that shouldn't be taken seriously, but that's the thing. Transgender people have been struggling with these issues for their entire lives, so to "normal people", the movie is just making light of people you've never met, or that you seldom encounter, so it's not serious.

To a transgender person, the role is making light of your entire life, your core identity as a person and the core struggles you've had to deal with since childhood. It's shoving how you're afraid people view you right in your face, as a joke, which most people will find hilarious and walk away from the movie with reinforced stereotypes.

You can do blackface, or make a joke about black people liking chicken and watermelon, or grape soda, and it's fine. It's in poor taste, because racism, but it doesn't ring true.

If you made a role that was a black people being a shitty worker, always stealing things, talking like a slave on a plantation, and in the end he realized he just didn't belong and should go back to Africa where he will be accepted, It rings true.

It's metaphorically equivalent to make a comic relief role where the character is a warped version of a transgender person.

Someone would be crucified if they made a role like that in a movie, not if its a transgender character though, because let's be honest, everyone would rather think to themselves

"God why can't there's people just fuck off."

Than even consider that they might be wrong.

I can only hope that Cumberbatch chose this role knowing it wouldn't come across that way in the full movie. I really like him as a person from what I've seen of him in interviews.