I have had similar experiences like that. The most memorable one, however, was similar to Uncle Leo in Fallout 3.
Her (or his) name was Aunt Lilly (I think). She lived a quiet life in Jacobstown in New Vegas (I think). She tended to her Brahmin stock and mistook me for her grandson. I met a nice human doctor trying to help these Nightkin with their mental afflictions. I decided to help out and enlisted Lilly's help in retrieving a broken Stealthboy. Once the scientist/doctor had it, he asked me to see if Auntie would help. She did. Nothing bad happened. Then, the kicker came when she left and he talked to me further. He wanted her to wear the Stealthboy all the time and he'd monitor her readings. I felt uneasy as soon as he said "all the time". Up to this point, she'd been managing her instability with medication and was quite pleasant to be around. So, my first concern was for her mental state. He told me flatly that she'd have permanent brain damage, but that the readings might someday provide a stopgap, even a cure. Thing is, the damage done would be irreversible. She'd never be cured. I felt horrible deciding for her, so I went and asked what she thought. She seemed so happy to help and volunteered immediately. Despite the fact that I told her that she'd be permanently crazy, she didn't care. She'd lived a nice long life, and if sacrificing her sanity meant one day helping further the development of a countermeasure or cure, she was all for it. I just stood there with the textbox open, debating whether I should just flatly tell her that I won't allow it, or let her. Eventually, I felt bad arbitrarily deciding, even though she wasn't all there to begin with. I let her and ran as fast as I could from Jacobstown without once looking back. I had just let a nice mutant who probably didn't have the mental capacity to decide choose to go crazy for the sake of others. I kept thinking of how I could become a mutant and take her place. It felt like the nice grandmotherly side I'd seen had been murdered, and that blood was on my hands. I then lost myself in the whirl of combat and carnage.