> macro hygiene in itself is a solution looking for a problem

No. Unless you're not familiar with Lisp-1 vs Lisp-2. In Scheme, you would have to GENSYM every variable in addition to every function you call within a macro. Whereas in Common Lisp you just need to GENSYM the variables. That's the real reason Scheme doesn't use DEFMACRO.

I'm not personally a fan of any hygienic macro system because learning a new language defeats the purpose and elegance of Lisp macros in the first place. But then again, outside of personal projects and academic exercises, no one should be using macros. Messing with fundamental semantics of a language while other developers are working on the same project will certainly make you a ton more enemies than friends. I still have a grudge against the guy that used Ruby's method_missing and I spent an entire day hunting down a method that didn't exist. When I figured it out, I don't think I've ever been so pissed at someone before.

I think in theory they’re orthogonal but in practice the two go together. It’s all fine and dandy when you’ve got a restricted set of battle tested macros from a single library interacting in real world code, but it rapidly breaks down when you’ve got application authors of various skill sets all contributing their own macros because the dare not touch the ones that came before. Macro hygiene provides the equivalent of type level guarantees to metaprogramming scope.

Macro hygiene is a solution to the problem of functions being in the same namespace as variables, together with standard, oft-needed library functions having short names that are easily chosen as variable names.