"A virtue untested is no virtue at all". That's what came to my mind reading your post. Quite touchy topic, takes a lot of guts to write about this. But, indeed, it's very easy to say I would never when you were never in a position to be asked to do that particular thing. There's no knowing what evil we're capable of doing until we're tested... and all we can do is hope not to get tested.
To answer one of your questions - I might refuse some treatment that caused terrible suffering to be obtained - I might, I cannot be sure. (Feels good to take a moral stand.) But that's only goes for my person. If one of my children needed that same treatment, I'd have no qualms about the suffering inflicted upon others - past, present or future! It's not nice to say something like this, but, since we're talking extreme situations, it is honest!