Lisp isn't solely defined by DEFMACRO. There are other reasons to use it too, in ways that can complement or compete with DEFMACRO. I also don't really know or understand what the term "flexible" is supposed to mean precisely. What makes a Rust macro less flexible than a Lisp macro in the context of this discussion? In particular, what do Rust macros tamp down on in terms of power that make them more justified for occasional use compared to a Lisp macro?

Lisp has a handful of language features that allow the definition of new syntactic abstractions: form level (DEFMACRO) and character level (SET-MACRO-CHARACTER). Just like it has operators to define new data structures (DEFSTRUCT and DEFCLASS). Just like it had operators to define new functions (DEFUN, DEFGENERIC, DEFMETHOD). Each of these defining forms materially change the way a programmer writes code. You don't need to add new syntax to change the language, and each kind of language change comes with its own tools and practices for working with them, debugging them, documenting them, and so on. All of this is to say: I don't see a good reason to have all of these remarks about syntactic abstraction when they very well could be made about data abstraction or control abstraction.

A useful language feature isn't something that needs to be maximized in idiomatic code. Syntactic abstraction is useful when it's useful, and when it is useful, it's usually extraordinarily useful—typically because a new syntactic abstraction allows a programmer to specify something much more directly or correctly than otherwise. (Other languages frequently resort to external processors or code generators to the same effect. Anybody who has used them knows how frustrating and difficult to debug they can be. But nonetheless, it's not that people do or don't want syntactic abstractions—they clearly do—it's more a matter of how accessible we want to make it to the programmer.)

I did not suggest disallowing it anymore than I suggested we should disallow the definition of new classes in Java. Being judicious and deciding when it's worth it is key, and there are few general statements we can make about this without additional context.