Derrida is amazingly difficult to understand at points, at others less so. What has become clear (!) to me is that Derrida is not for an unconstrained, undetermined free-play of meanings, but simply has a more-complicated-than-usual view of the context of meaning-making. An important role is played by what he calls the language police:
But there are, first of all, several ways of invoking or of specifying the rules. There are ‘theoretical’ grammarians, linguists, and jurists who state, describe, explain the norm without insisting upon its application, at least is immediate application, by force (physical or symbolic). Other functions consist in eliciting respect for the law and in disposing of a force deemed legitimate to this end. These two types of function, these two ways of ‘fixing’ rules and also, to take up your expression again, of ‘fixing’ the ‘contexts of utterances,’ bring together in a single person the theoretician of right [droit], the legislator (the inventor or first signatory of a constitution himself, or those in whose name he claims to act), and the executive power. (Limited Inc, 134-135)
There are, thus, interpretive police for all language, constraining its meaning. Derrida even goes on to provide a concrete example!
But every institution destined to enforce the law is a police. An academy is a police, whether in the sense of a university of the Académie Française, whose essential task is to enforce respect for and obedience to [faire respecter] the French language, to decide what ought to be considered ‘good’ French, etc. (135)
So at last, I continue to be persuaded that Derrida is not an obscurantist terrorist, but simply a critical idealist of a deeply Enlightenment sort, even where or especially when he is calling this tradition into question.