The problem is the fact that the brass needs to expand and grip the chamber walls for two reasons.
1. Seal the chamber so the hot, high pressure gases go forward and drive the bullet and do not rush rearward where they can cause serious problems including hurting/blinding the shooter.
2. Grip the chamber walls so the thrust of the case head against the bolt/breech is not excessive.
Reason #1 is why case head blow outs are so dangerous to the shooter. This is mainly a problem with bottlenecked rifle cases, but can happen with any case.
Reason #2 is sneaky and does damage a little at a time until something fails.
I don't want to hear about special circumstances where experienced reloaders lightly lube a case.
