Derrida logic:
We always see language and writing together. Therefore, language is writing.
Compare:
We always see Abbot and Costello together. Therefore, Abbot is Costello.
Or even:
We always see logic and fallacy together. Therefore, logic is fallacy.
That he would like that last one makes no difference to the point.
Constant co-appearance is not an index of potential reduction to identity. Exactly to the contrary.