We know how to package functions and data structures in modular, reusable ways; we don't know how to do that with macros, so macros hurt code reuse.
-- who's "we"? But the post itself is interesting evidence for what one could call Graham's Thesis, the idea that any programming language as powerful as Lisp is isomorphic to Lisp; or that all programming languages can be defined by the subset of Lisp that they exclude. The author argues that this exclusion is necessary and good because it gives a language a distinctive character around which a set of idioms, and therefore a community, can develop more easily.
While I totally agree with Kenny that the author's claims about Lisp have a ring of inexperience to them, I do think that this social/communal prism is an interesting one and that Lisp has some distinctive qualities in this area as in others.