The assertion that the female flight attendant can't wear jeans and T-shirt is a non-sequitur, because there is a uniform for that position and it isn't jeans and T-shirt. Besides, plenty of women wear jeans and T-shirt and aren't projecting male gender.
It wasn't about "projecting male gender", it was purely an example of unprofessional attire at work. Indeed, there is a uniform, but in many cases there is no official uniform, and instead there is a "dress code". That applies to trannies equally.

But the choice of what gender to project is none of anyone's business but the person making that choice.
So are you saying that a male airline worker can choose to wear the female uniform and not be presenting themself unprofessionally?

I don't accept the goth statement, because I don't recall hearing of hundreds of years of persecution against goths.
Goths are discriminated against. How long this has been happening is irrelevant, discrimination isn't worse just because it's been happening for a longer amount of time. Again, this is about dress. Goths have a particular style of dress, and it would be considered by most employers to be inappropriate in the workplace. Refusing to hire someone because they are a goth is equally as bad as refusing to hire someone for being a tranny. At the same time, telling a goth they cannot dress as they please in the workplace is equally as acceptable as saying the same to a tranny.

I can't think of any time in my life I've heard widespread use of the word "goth" as derogatory
Seriously? You work in a university and have never observed discrimination against goths? I find this extremely surprising.

Whereas "gay" once meant happy, and has turned into meaning generically "unfavorable."
"Gay" to me simply means "homosexual", although the word can be used in the context you describe.

When it gets to the point that the social norm is to think certain minorities shouldn't be allowed to work certain jobs
You seem to be suffering from selective reading. I'm not suggesting certain demographics (this isn't about minorities) should be excluded from jobs, just that they should act in the same professional manner expected of all other employees.