Sometimes (rarely I would say) I press
C-w by mistake and if the mark defines a non empty region, it gets deleted.
The few times this happened I just pressed undo, but I am afraid that sooner or later I will delete something without noticing.
Is it possible to tell emacs not to delete a region if it is not selected? It never happened to me to wanting to kill a region which was not selected, so this workaround would fix my problem.