Yeah, that would be sad. Luckily, I'm not one of these people but at the same time, there's no denying that keyboard is
the main modality most Emacs interactions are optimized for.
Your example of auto-completion is actually a good argument in favor of keyboard use since I cannot think of any other modality where a similar functionality could easily be implemented.
That said, I'm not arguing that keyboard-based interaction is per se superior to any other form of input. But to me, it's undeniable that Emacs is de facto a keyboard-centric editor. And let's not forget the history of the software: it was originally developed when terminal-based interaction was the norm, (wide-spread) use of mice came much later.
