The argument you're having is exactly why blameless post-mortems are so difficult to insert into existing companies. Shifting from a desire for "justice" to "doing what's best moving forward" is really hard for a lot of people.
There is a segment of the populace who feels that every "wrong" must be "punished", and they generally make life miserable for everyone else. Usually no one will speak up for fear of being punished along with the "guilty".