I seek a word for the expectation that any arbitrary group of people can be held morally accountable as though they're a single moral agent

I think this must be a cognitive error of some kind. I just now read the phrase, "the hypocrisy of the left", and it occurred to me that hypocrisy is a moral action, which can be taken only by a moral agent, ie, a person. And "the left" (or "the left wing" or "the political right") are not persons; they don't have stable personalities, they're not moral agents, they can't engage in hypocrisy.

Is there a word for this kind of error, calling on a (usually ill-defined) group of people to exhibit a stable personality and moral accountability?

Single-word request requirements:

• Sample sentence: "You get an F for your paper entitled 'The Sins of The Right', because it's based entirely on a cognitive error known as homunculus-ex-vulgus."
• Not being sure where to start with a dictionary or thesaurus, I've tried googling misattribution of moral agency and cognitive error moral agency, also group single personality; I went through 50 Common Cognitive Distortions on Psychology Today. I haven't found anything that even sounds similar.
• My criteria for choosing the best word: If it's a clinical or technical word, then I guess the best word would be one that literally means what I'm talking about. If metaphor is the only thing available, I guess the best word would be the most neutral-sounding, the least baggage, the kind of word that wouldn't put people on the defensive.
• Words I've considered: honestly, homunculus-ex-vulgus fallacy is the only thing I've come up with.
• A compound word or phrase is fine. Cheers

P.S. I would be most grateful for any feedback concerning the downvotes.

Solution 1:

I believe you are looking for the term metonymy, a word or phrase that represents a thing, or concept. The expression ‘the left‘ simply stands for [members/supporters of] the left wing [political party].

Other examples of metonymy,

Crown - in place of a royal person
We will swear loyalty to the crown.

The White House or The Oval Office - used in place of the President or White House staff
The White House will be making an announcement around noon today.

Heart - to refer to love or emotion
My dear, you have all of my heart.

Dish - for an entire plate of food
That fancy fish dish you made was the best of the evening.

Source: Your Dictionary See also Merriam-Webster's explanation.

Whether or not you agree that members or supporters of the left are hypocrites that is a separate political issue.