Moral responsibility of the community

لَّوْلَآ إِذْ سَمِعْتُمُوهُ ظَنَّ ٱلْمُؤْمِنُونَ وَٱلْمُؤْمِنَـٰتُ بِأَنفُسِهِمْ خَيْرًا وَقَالُوا۟ هَـٰذَآ إِفْكٌ مُّبِينٌ

Why, when you heard it, did not the believing men and believing women think good of themselves [i.e., one another] and say, "This is an obvious falsehood"?