This should be fucking obvious but an argument I just went through on Twitter (gods I really should just not get on twitter) tells me that even left-leaning people for some reason sometimes think they are owed this information simply because they are interested in flirting.
Transpeople have no obligation to out themselves. even if you have or are going to kiss, or date them.
To think otherwise is to assume you are owed knowledge about their body. To get upset after they do tell you is to assume you were entitled to continue the relationship, or that they were trying to manipulate you.
If you have hangups that would prevent a relationship it's on YOU to be upfront about them or to accept the potential disappointment with grace.
I don't think she's suggesting it as something to drop after you've been married for twenty years, but also not something to have to give to people unsolicited regardless of whether you are starting to pursue a relationship or not.
If you are pursuing a relationship with someone, it's a pretty important detail. Not like the first thing out of your mouth, but pretty damn early in the dating process.