All abstractions can make your code unreadable; the key, as always, is to create good abstractions and document them clearly. Macros are syntactic abstractions. It's just as important to document them as it is for functions or objects. Of course, if you just have a little local macro that you're using for convenience, looking at the implementation may be sufficient. But when you write a macro that you want to share from a module, rather than requiring your clients to read the implementation, you document the syntax and the semantics, just like you would if you were writing a separate language.

But by having macros directly in JS, instead of having to use a whole language that compiles to JS, you can combine syntactic features from different sources. For example, right now there's no way to use one feature you like from CoffeeScript with another feature you like from TypeScript. You just can't combine them. But with macros, you could import two different syntaxes from two different libraries and use them in the same code.

On top of that, if we actually had macros in a future version of the standard, you wouldn't even have to precompile the macros offline, and you wouldn't need a preprocessing step at all. (For latency purposes, you might want to preprocess macros offline as an optimization. But for development, not having to do a preprocessing step is more convenient.)

Dave