The points that you (and other commenters) make is ultimately related to the fact that when a person being shunned belongs to an outgroup, they are categorized

The points that you (and other commenters) make is ultimately related to the fact that when a person being shunned belongs to an outgroup, they are categorized as a representative sample of the group. In other words, the entire group is assumed to be consisted of homogeneous individuals, exhibiting roughly the same behavior as the one being discredited. However, if said person were to belong to an ingroup, then said person is categorized as an outlier by its members. We can see lots of such examples in politics, such as people casting similar aspersions about how the recent action of a single person in an outgroup proves the larger aspirations of said group, about how "they're out to destroy society", and the like.