If instead of 'mass formation' we say "collectively, their minds are strongholds of poisonous, madness and hate inducing ideologies' what has happened to them becomes clearer.
But, as you know, your description covers only a part of what is going on with the "mass."
The mass formation is like a giant lynch mob in the way it acts. It is significantly more complicated than saying "collectively, their minds are strongholds of poisonous, madness and hate-inducing ideologies" though that statement is absolutely accurate.
As a mob, it builds a mote around itself that prevents any dissenting opinions from entering the "mass." This creates an echo chamber that provides a ripe and nurturing environment for an explosion of brainwashing.
And there is a shallowness of thought by individuals inside the mob that prevents them from discovering differences between the component member groups that might cause conflict or otherwise damage the group (take feminists vs trannies for example).
A major feature of the "mass formation" is the way individuals are subsumed into the group. Individuality is abandoned for groupthink. A person's identity merges with the collective identity.
The mass formation is organic and grows like a biological organism. And it doesn't just hate...it will eventually apply that hatred in the destruction/murder of its enemies.
Here's a book that covers this matter brilliantly: