Your text is saying that populism creates dichotomies instead of acknowledging the naturally varied rainbow that exists in any group of people. Here's how I would handle it:

"Populism sets up the people as an 'object' based on organicist premises that incorporate it as part of the State and deny its plural manifestations, turning core differences into stark oppositions that divide the people/populace into 'friend' and 'foe'."

Notes:

- "Sujeto" in Spanish sometimes means 'object' in English.

- 'organicist' has a very specific meaning. See the Merriam-Webster definition:

Main Entry:or£gan£i£cist
Pronunciation:-_s*st
Function:noun
Inflected Form:-s
Etymology:International Scientific Vocabulary 1organic + -ist

: an advocate of organicism *the organicist believes that every actual event in the world is a more or less concealed organic process— S.C.Pepper*
–or£gan£i£cis£tic \(|)*(r)|gan*|sistik\ adjective


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Note added at 47 mins (2010-08-09 07:07:23 GMT)
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Instead of 'incorporate', better to say 'regard' because 'part of' captures the idea of 'reify'.

"...premises that regard it as part of the State"

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Note added at 48 mins (2010-08-09 07:08:56 GMT)
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BTW, in Roget's Thesaurus, one of the relatively few synonyms of 'manifestation' is 'unfolding', which is the literal translation of "despliegue".