Anyone else getting hints of the Force lol, im just reading through your comments (tbh ive never read the books so never knew about this) an it all sounds bit much like Kotor, prob just me
It's complicated. And extremely dangerous. Doing such a thing will actually leave a Tranquil vulnerable to possession, as well as do nasty things to the Veil.
It's a great book with some memorable (and controversial) characters, as well as a few familiar faces. If you'd really like to understand, you need to read the book and decide for yourself.
I doubt Anders will feel bad about Karl. At the time, there really isn't anything that could have been done and Anders did know about acceptable losses. While he would (probably) support this solution for Tranquility, he'd likely be aware that he did what he had to.*
*If the player kept him alive, that is.
Also, I know this cure had been very hush-hush and few knew about it. Without giving too much away, only after Asunder do the mages (and Templars) know about this. Even then, I'm still wondering how much word has really spread. Another non-spoiler I can give you: The Circles and the Templar Order are very disorganized after Asunder, so I'm not sure how well communication is working. There is a lot of mages on the run now; a lot of templars out for blood. How much is known and how much is hidden remains to be seen.
For what it's worth, I think the Chantry would do their part to keep the cure hidden or severely downplayed. I really don't think that the Chantry wants it public knowledge that Tranquils can be cured and the average Joe the Farmer in Thedas wouldn't want know. Sure, there would be rumors, but I think most would rather believe the Chantry rather than face such a weird and (to some) a very frightening reality.