GUESTS are not a group. A GUEST is someone who is posting but who is not signed in as a member, for a variety of reasons, mostly quite good reasons. There has never been any animus shown to people for doing that as such.

A few individuals when coming in as GUESTs have some hang up about even identifying themselves with a temporary name or number, which would make it more convenient for other people to respond to what they are saying. This is seen by many people as intentional discourtesy, when it is done intentionally. It may well be that sometimes the people who do this are in fact members, but that doesn't make any difference either way.

While there may be some people who do this for some mysterious reason, but without having any hostile intention, there have been many cases where it is clearly done with the intention of sowing discord. This explains why there is a fair amount of antagonism shown to the practice.

Suggesting that people who post without any kind of tag are "a group" subject to unfair discrimination makes as much sense as saying that people who drop litter are a group.