Some of the arguments against having a trans person on the show echo what I heard in the 90's regarding why they shouldn't have a gay crewperson. "How would you even know when no one would have a reason to say it, we've probably seen a ton of gay characters and just didn't realize!" This logic only holds if your mindset (consciously or unconsciously) is that being gay is something where the default is to hide it, and thus ignores all the ways sexual orientation would come up casually in a world that has evolved beyond homophobia. In the lead up to Discovery, I don't think I've seen a single person express that concern about Stamets, because now we see that it's actually quite easy to establish a gay character in ways that are not distracting.
I think it would be similarly easy to have a trans character on Discovery, you don't have to do anything beyond just putting a trans actor in one of the roles. Most people will get it. Eventually, organic ways to reference the character's backstory and the fact that they're trans will present themselves.
I think having a gender fluid alien, while maybe providing some representation to gender fluid or maybe non-binary people, is really an easy excuse to keep ignoring the issue. It would be like having some wacky alien instead of Uhura or Sulu, while pretending they stood in for African-American or Asian people. It's really insulting to people who don't get representation. It's like tossing a tic tac to a starving person and acting like it's okay. If you've seen people like yourself on TV forever then you really can't understand this.
I've started thinking the ideal approach would be to do both, actually -- you have a trans actor in the cast as a human character, their presence is matter-of-fact and unremarkable, Uhura & Sulu style. Then you also eventually do a "Rejoined" style episode that lets you actually do a story about transphobia, in the classic Trek-alien-allegory style.
Profit and Lace gets misread far too often and easily. You are ignoring the position of Ferengi Women in the show, ignoring the general portrayal of women in Trek, and particularly Quarks specific narrative history as a character in relation to those things. (It's an inversion of his storyline with Pel for a start.) it's a lazy reading on a show that has Jadzia Dax and Kira Nerys in it.
Here are some messages from "Profit & Lace":
1. Threatening a woman's livelihood to coerce her into sex is OK -- she's ultimately going to like it
2. Attempted sexual assault can be hilarious!
3. Women! They just can't stop crying all the time, am I right?
I feel like I could go on. It's really not lazy to critique this as a sexist hour of television. DS9 got a lot right with their female characters and is not a sexist show generally (I actually quite like "Rules Of Acquisition"... the A story, at least), but that doesn't give them a pass. In much the same way that TNG was not generally a racist show, but "Code Of Honor" can still be a racist episode. The fact that "Profit & Lace" is nominally claiming to be about equal rights for Ferengi women is just a fig leaf.
IMO if you want to show real progress then a Transgender character should be either a villian or a asshole. I've always felt the best way to present progress is to show people of color,gender who are different that they are capable of being terrible people just like everyone else.
Great progress is when you can have a Transgender character get to be like Denzel Washington in "Training Day" as oposed to being relegated to the PC nice guy/girl who is written so safely that they won't offend bigots or liberals who get offended at the first sight of something controversial.
Well Rounded characters are always going to be more intresting than characters who's only purpose is to be a role model.
I take your point generally, but it requires a certain critical mass of trans characters to start with. When there are very few of them anywhere in the entertainment universe, you're not yet at the point where presenting them as villains can be touted as progress. Also, I think it's a false choice between villain/asshole and perfect saint -- there's a middle ground you want to hit. I actually think Laverne Cox's character on "Orange Is The New Black" is a perfect example of how to do a trans character properly... she is definitely a flawed person, she is not some PC paragon of morality, but she is no better or worse than anyone else in the cast. What's meaningful is portraying her as someone who is as fully human as anyone else.
Geordie was blind, but was able to use the visor. The only character I recall using a wheelchair was Pike and that's arguably more a mobile life support system. It would be interesting to see a Stephen Hawking type character.
There was also that reverse-aging admiral in "Too Short A Season." And Bashir's love interest in "Melora."