> Why should they demand that GHC generate readable C if it were generating C instead of assembly?

Debugging in programs that are mixed C and other code. If you're in the middle of debugging Firefox (or any composed system) and start stepping through unstructured gobbledegook, you'll end up cursing the people who did this to you.

This becomes less of an issue if/when the non-C language becomes so ubiquitous that there is proper debugging support for it (viz Python or C++ support in gdb), but as long as a bug may be triggered, propagated or otherwise be interacted from the non-C side, you want that code easily readable.