The trouble is this: when “leftism” becomes an identity element, it makes leftist politics involuntary.
c.1600, "sameness, oneness," from Middle French identité (14c.), from Late Latin (5c.) identitatem (nominative identitas) "sameness," from ident-, comb. form of Latin idem (neuter) "the same" (see identical); abstracted from identidem "over and over," from phrase idem et idem. [For discussion of Latin formation, see entry in OED.] Earlier form of the word in English was idemptitie (1560s), from Medieval Latin idemptitas. Term identity crisis first recorded 1954. Identity theft attested from 1995.
identity i·den·ti·ty (ī-děn'tĭ-tē)
The set of behavioral or personal characteristics by which an individual is recognizable as a member of a group.
The distinct personality of an individual regarded as a persisting entity; individuality.
The element of a set of numbers that when combined with another number under a particular binary operation leaves the second number unchanged. For example, 0 is the identity element under addition for the real numbers, since for any real number a, a + 0 = a, and 1 is the identity element under multiplication for the real numbers, since a × 1 = a.