I don't know what Sir Pterry would think today.
I am 100% certain that he would engage in civil conversation and discussion and that is it.
I don't actually see that it matters either way, because I have not arrived at my present point of view to in order to imitate any famous figure. I read different arguments. If there was an essay by Sir Pterry on why he supported trans activism, I'd certainly be eager to read it and see if it convinced me, but I wouldn't change my mind without reading it!
Clearly, people read stuff through their own lenses. I have all the Discworld books, the Trucker books, the Johnny books, Nation and so on. Quite keen on his work, you might say.
To me, as a feminist, Monstrous Regiment is one of my favourite books and it seems incredibly GC. I re-read it again and again because I find it cathartic. We have a bunch of girls in a very oppressive, sexist society, who cross-dress to escape its confines, all of them thinking that they're the only one who wished they had the same freedoms as boys, and all with separate, personal priorities. It also has the Homes for wayward girls, which draw on real world events, and there are sexually abusive men who prey on girls from there. There is a line there that haunts me from (I think) Tonker about one of the men who abused them, after Polly says he seemed nice.
"Yes. He was good at seeming".
And at the end, they all stand up and insit on having their achievements recognised as women. I love that so much.
Twitter shows me that many people read in a totally different way, and well, what's the point of arguing about people having different eyes and experiences?