It suits our general pattern of thinking, I would assume. Categories are are what we utilize to make sense of the world. This probably boils down to a general discussion about semantics, but what use in clinical psychology, for example, is categories. We open drawers labeled with one or more certain terms, put in a file card with a name on it and close it. Until we need it again and sort it differently, the name will stay in that drawer.
With regard to the writers piece and your comment, it seems that the message is intended do discard a certain kind of people. If not discarded as being as a whole, their thinking certainly is.
Hypothetically, the writer felt the urge to make sense of his/her own world. Meaning, he/she gains a sense of security by "convincingly" refuse the probability that a certain amount of Olivers are/may be right.
I do not know who the writer feels associated with. I would simply go with the belief that he/she met too many batshit crazy people with the name of Oliver.
Just my thoughts. Thanks for the comment.