I feel that the source of prejudice has completely natural and unavoidable source – like the article says. We cannot avoid making assumptions, this mechanism is what keeps us safer in a very complicated an pretty dangerous world. We need schemas for people – we identify them as part of bigger group. And we have certain stereotypes (be it good or bad) about that group.
Not only that – everyone also identifies as a member of some group (we are all students, we are polish, we have certain gender) and also has an image of that group in their minds. We stereotype ourselves.
The stereotype about a group can sometimes be hardly distinguishable from real knowledge about that group. And we need knowledge, our natural tendency is to accumulate knowledge that’s relevant to our lifes.
I encountered many situations like those in comics. People who were treated badly often react with anger and it is likely to be directed into a group rather than a certain person. I feel like it is especially the case in the internet where we do not see faces, real identities but we recognise an argument and we think this argument “belongs” to a group. And then we may just think “oh this *name of the group* talk stupid again.
Also it is easier to remember bad things about the group that is different to ours, that we may disagree with or find weird.