"The critical task for feminism is not to establish a point of view outside of constructed identities; that conceit is the construction of an epistemological model that would disavow its own cultural location and, hence, promote itself as a global subject, a position that deploys precisely the imperialist strategies that feminism ought to criticize."
Butler is saying that construction of identity does not deny one agency. She is saying that feminism ought to seek ways to work within the constructions that illuminate the inconsistencies of the constructions. To attempt to act outside of the constructions of identity is to act without a cultural identity, presumably as a universal subject. To portend a global point of view one must exclude certain people, essentially pushing them into another margin. This exclusions are what Butler would argue are "precisely the imperialist strategies" that should be avoided.