Our issue with the turn editing on is that instructors who copy and paste from a course with editing on tend to copy and paste the UI controls. Then when they save, there are phantom UI controls that confuse them. Instructors who copy and paste text from a course that has editing off will not accidentally copy UI controls.
My worry is that if editing is always on, they then will copy and paste the UI controls by accident more frequently.
So if you remove the editing on/off then you really should add something to the atto editor's clean paste function that strips out anything UI-related that shouldn't have been copied.
We do try to train people not to copy and paste from one course to another but instructors do not always listen. It's easier to them than doing an import from a previous course.