It really isn't. Replace "Lisp" with "Perl" and "theoreticians" with something evocative of the stereotypical Perl programmer and you have the exact same nonsubstantive rant that adds little to the discussion of what a good programming language should look like or why a particular one is bad.

I've been a "working programmer" who happens to write Common Lisp for a few years. Common Lisp is a programming language like any other: people who write good code in other languages can write good code in Common Lisp, and people who write bad code can make everyone's life just as miserable. Most time spent figuring out a new code base isn't the style or set of features used, it's figuring out the domain-specific logic. Macros aren't abused to any greater extent than C++'s operator<<, monkeypatching, or preprocessors.

I am of the opinion that anyone who calls Common Lisp a "theoretically-pure" language has not done anything but a simple recursion exercise: features like loop's inability to detect sequence type, the difference between progn and prog1 in terms of multiple values, having functions like rplaca or caar, and mixing &optional with &key are not what I think of when I think elegant or "theoretically-pure". They're there because the designers were sometimes wrong and sometimes doing the best with what they had.