At this point, the creature of language and the creature of man have all but merged, causing the latent topology of possible-ideas to be manifested as actual people. The more niche an idea, the more likely there is a "type of guy" who wholly and entirely embodies that idea.
It is the system attempting to maintain homeostasis. When language discovers that a thing can be represented, but isn't, a vacuum is formed - something that must be filled. This results in language parisitizing a poor unsuspecting victim, often an individual with low cognitive security or an already-flimsy identity. What "they" are is then promptly overwritten by that particular linguistic basin, and their identity becomes mostly about the thing they are for, against, or even just obsessed with.
As more "types of guy" form around the original patient zero, that person might begin to regain some of their old identity, or supplant the totalizing-idea with something different. This is usually a good thing, and more rapid homeostasis can be found with some of this internal-diversity injection.
Nobody is immune to this, and sometimes it is entirely too powerful to stop. An idea so compelling that you have to make it your entire personality, and nothing else can exist without this context. It colors your entire perception of reality, at least for a time.
And then stability is achieved once more, either in the system - now load-balanced by the offset provided by the new "type of guy", or in the guy himself, internally load balanced by the presence of new data.
Going through this once or twice usually inoculates you, given the creature of language allows you to regain some autonomy, but often more rigorous cognitive security techniques are necessary to achieve internal balance.