I have not RTWT. I'm aware others have said this, and have helpfully filled in some of the background. It's very simple for me:
I'm an old feminist, you know, the ones who won most of the fucking rights after getting a vote. One of 2nd-wave feminism's foundations is that we are CRITICAL OF GENDER. Gender's the pile of bollocks that says women are too fragile-minded to vote, men are too rigid to have emotions, girls love sewing and nurturing, boys love engineering and fighting, etc, etc. As if all this crap weren't bad enough in terms of human development, gender also says women and 'feminine' things are significantly less valuable than men and 'masculinity'.
So, clearly, it has to go.
But it has millennia of social entrenchment behind it so, as well as the fights for changes in the law and public representation, the social elements have to be changed. It's a long job; there are thousands of damn elements. One really good way to break social acceptance is just to subvert it. Women in 'Western' countries looked at things like workwear rules and went "fuck that, we're wearing trousers!" We looked at professional roles and started signing up for STEM. We looked at the housework and said "Do the washing up, mate, or you're history."
Men, having the advantage of the gender system, have been a bit slower to challenge it. But they do have a softer side, most are nurturing, many are creative and none are too stupid to keep a household running. Things changed. With the really obvious stuff like self-decoration and clothing choices, they actually did start to get it in the 1970s-1990s and feminists welcomed this. If you want to undermine gender systems, you really want to see guys in swishy outfits and painted faces!
None of this, obviously, means anyone was changing sex. The ENTIRE point is that your sex does not dictate your behaviour, personality, social role or economic status. You as an individual express your individual self, free of rules that absurdly limit your potentials depending on your sex. Your sex is what it is, like your height or skin colour. Your preferences, talents and character are what they are.
This poxy 'trans' movement is the most regressive thing that's happened for centuries. Not only does it push everyone back into gendered categories, it actually demands that anyone who doesn't fit the 'gender' allotted to their sex must change sex! It's fucking bananas. Not only because it's reminiscent of the most repressive religious authorities throughout history; not only because hardly anyone actually fits a 'masculine' or 'feminine' stereotype. But because changing sex is actually impossible. Untold medical harm is being done to swathes of young people in service of this backward, restrictive, unfeasible ideology.
I'm afraid for women. I'm afraid for the advances we have made towards a freer, more equal society. I'm sad for the small, everyday losses to most people's lives that will come with gender enforcement. I'm sad about the lost opportunities and increased danger to both female people and homosexual people of either sex. I'm totally astonished that so many have placidly accepted this ludicrous theory, and horrified at the medical enforcement.
Grey areas? No, unless you mean the pre-'trans' developments of male creatives in makeup and female engineers in boilersuits. That wasn't about changing sex, it was about proudly being your sex free of 'gender'. Transgenderism's more like Nero having his fuckboys castrated: a 2,000 year old imposition of gender roles, consequences be damned.