Here are a few quick references.
Feel free to provide counter references that indicate one should, as you espouse, leave finger on trigger once the gun is unholstered
3. Never Put Your Finger on the Trigger Until You are Ready to Shoot
While there have certainly been documented incidents where firearm accidents occurred even though no one pulled the trigger, negligent discharges mostly occur because someone pulled the trigger by mistake.
Eliminate that possibility by never placing a finger on the trigger – meaning do not have a finger inside the trigger guard – unless planning to fire the firearm.
ALWAYS Keep Your Finger Off The Trigger Until Ready To Shoot
When holding a gun, rest your finger alongside the frame and outside the trigger guard. Until you are actually ready to fire, do not touch the trigger.
Rule 3: Keep Your Finger Off the Trigger Until You Have Made the Decision to Shoot
This rule is about trigger discipline, a key component of responsible gun ownership. By emphasizing this principle, we aim to prevent accidental discharges. Maintaining trigger-finger discipline is imperative to safety and shooting success. Guns do not simply “go off.” They are made to fire. A very specific sequence of actions must take place, and that sequence ends with the operation of the trigger. Very rarely will a gun fire if the trigger is not pulled.
RULE III: KEEP YOUR FINGER OFF THE TRIGGER UNTIL YOUR SIGHTS ARE ON THE TARGET
Rule III is violated most anytime the uneducated person handles a firearm. Whether on TV, in the theaters, or at the range, people seem fascinated with having their finger on the trigger. Never stand or walk around with your finger on the trigger. It is unprofessional, dangerous, and, perhaps most damaging to the psyche, it is klutzy looking.
Rule Three:
Keep your finger off the trigger and outside the trigger guard, indexed along the frame or slide until you are on target and have decided to fire.
Rule #3 - Keep your finger straight and
off the trigger (and if available, the
weapon on safe) until you are aimed in
on your target and ready to fire