Those who parse everything through a group mentality -- at least, the more clever ones --
have to ask this question because their association with said group "stains" them with any sins committed by the group.
They can either conclude the group was always evil but did a better job in the past of hiding it, absolving the individual of their own association.
"I may have been a part of that group, but I didn't notice they were evil. I was just following orders. I'm innocent".
They can conclude the group became evil and was once good, preserving any good deeds this person did while associated with the group but condemning any behavior post-evil-switch.
"I may have been a part of that group, but they didn't become evil until after I had already cut ties with them. Not only am I innocent, but I am more perceptive than the people who stuck with the group after they became evil."
Or they can conclude all groups are a combination of individuals who are each ultimately responsible for their own behavior and their own participation in the group.
"I was a part of that group and I didn't take responsibility for my actions, which led to my own negative behavior. I now am better equipped to perceive these situations and to avoid them in the future."
This latter conclusion does not jive with the
types who tend to congregate in ideological/political mass movements.