It did sort of fall into the ignorance of the disease at the time and Carly's own ignorance, but Carly did have a medical background, so it just felt like a low blow for the sake of a low blow. Overall, not anywhere near the worst of Carly's action in the scheme of things lol
I despised Carly for how she treated Robin, but I still found her fascinating and quasi-rootable at that time bc of her neuroses, pathos and obsession with Jason. It was very real and relatable. That's the best of what soap characters can make you feel, conflicted as a fan. I was not particularly hardcore for Jason and Carly though, bc I'd never liked Jason much either lol.
I think JFP and Megan were determined to put their stamp on the show and make GH like their other terrible works as quickly as possible. That's why they went full force with Jensen Buchanan and Roy, and that's why cutting out the roots with characters like Carly and Emily served their purposes to supplant them. Of course, GH being the flagship of ABC was a bridge too far, and it didn't work. JFP never had that kind of power again.