Trams activists and allies really do think human bodies are like Lego and you can mix bits from different kits or put the bits you have together in different ways and it all joins up. It's so ... reductive and disassociative.
Counterintuitively, I think it's an outcome of people being more educated than in the past, and having access to more information.
We get the headlines when something works (like organ transplants or cloned sheep or inducing some elements of cross-sex secondary sexual characteristics using hormones) so we think we understand what's possible or assume it's a small jump to something else, when in reality we know very very little about the actual mechanics of what was done and how, the limitations, the risks, all the failures that weren't headline-grabbing. The Dunning Kreuger effect basically.