Emacs as git editor, what is Rebase mode?

When I run git rebase -i I get the absolutely horrible Rebase mode in emacs.

This only accepts some pre defined commads like

c -> Pick

r -> Reword

etc...

Even if I change to text mode emacs auto-magically makes the git-rebase-todo file read-only. How can I disable it?

The only solution I have found is to use vim as editor (something I don't want, I like emacs in general)

The rebase-mode automatic activation is triggered by the auto-mode-alist variable. You can try disabling it to edit git-rebase-todo files in fundamental mode (no special shortcut, no automatic read-only flag, ...) :

(setq auto-mode-alist (delete '("git-rebase-todo" . rebase-mode)
                              auto-mode-alist))

On another note, you might want to use magit to realize your git operation directly from within emacs.