There is a tendency to view “deconstructionism” as some sort of non-logical, random assault on reason and logic. It is not. Postmodernism (of which deconstruction is one element) pays attention to the medium itself; it is a self-awareness of the act of creation. A parallel in the physical world might be a carpenter who, in the process of making things out of wood, makes a wooden workbench. And, keeping with the carpenter analogy, a de-construction of a house to see how it was built would reveal more than the house’s style, size, or neighborhood—it would reveal how the structure was supported, and the building techniques that the architect chose for his creation. The key word for both carpentry and literature is “structure” – how the work was constructed. Critics, when deconstructing a work, contribute to their specialty by making the reader (or occupant) aware of more than just the façade or siding or curb appeal of the structure. Modernism critique employs the techniques of deconstruction to tell us more about the work than we can see overtly. Theoretically, one could deconstruct the critique as well – this is done when world-famous scholars amass a body of criticism; other scholars then reveal the argumentive structures that the renowned critic used; Claude Levi-Strauss is a good example, or Fredson Bowers, the world-famous Shakespeare scholar. I’m not sure exactly what you mean by “undermining,” but the act of deconstructing a work is a strengthening, not a weakening, process — deconstructing 18th c. novels, for example, revealed the hedonistic, anti-feminine underpinnings of many famous works.