By stretching you mean, to push it beyond it's borders to open it further? Why?
Our doctors don't do this and neither do we, for the reasons you state, not to mention IT HURTS!!!!! Why mess around with Mother Nature in such a potentially dangerous and painful way?! And yes, I did see a reallllly bad cervical lac once (had to go to OR for emergency repair) on a patient of a dr who did this as a matter of routine about 7 years ago. It was horrendous. I am glad he is no longer delivering babies. The girl almost bled to death.
The only time we see our dr's "stretch" a cervix is to reduce a very friable anterior lip when a woman pushes. If it does not reduce easily, they stop right there and leave it alone.
You are right Dayray, to be concerned. As far as scarred cervices, I would leave that up to the doctor or midwife to deal with it. I personally would not stretch a cervix beyond it's borders to "force" or "help" anything along. I am very, very anally cautious, I know.