I keep seeing this. Why do people keep making the point that if you can make an accurate shot from 200 yards with a rifle that makes you a sane person?
People generally use really crude (and incorrect) heuristics when judging others. "He was a family man/good christian/nice to me at work/etc, I don't know how he could have murdered his family!" Mental illness gets it even worse b/c most people don't have any good framework for understanding it.
I think that's the mixup. You can be insane but still perform some very calculated plots.