> Why is it so hard to see that this can lead to an explosion of unreadable code if left unchecked?

Anything can lead to an explosion of unreadable code if left unchecked. Any language feature, with no exceptions. Variables, loops, functions, types - you name it. Anything can go wrong if used with a bit of imagination.

Macros, on the other hand, provide an exclusive way of eliminating this complexity. A way of eliminating degrees of freedom of what can go wrong. Nothing else is capable of doing it.

> Wouldn't you be concerned if you had to work on a huge code base where most of the code is written using macros?

I'd be extremely happy to be able to work on such a well designed project.

> I would run away, personally.

It only means that you don't know how to use macros. Nothing else.