A friend who shots a lot in competitions said only use one, but could offer no reason why.
When people suggest or mandate a course of action but cannot give a reason why it should be followed, then there is reason to question the validity of what they want you to do. They may be correct, or not, and the fact that they can't explain to you why you should choose a particular course of action indicates that they may not fully understand what they are talking about.
If the only reason you shoot is for target purposes, you should fix it.
I see target shooters do a lot of stuff I consider weird and they shoot very well. A lot of what I have seen does not transfer well to situations outside of target shooting, such as to self defense shooting. If you are only target shooting and it poses no safety problems while at the same time making your shots better, then I see no problem. People will give you grief for it, however.
That would be like using two feet to drive, breaking and gas.
No, it would be nothing like using two feet to drive. In using two feet to drive, the feet often need to be doing different tasks on different pedals, and those tasks are sometimes being accomplished simultaneously and at other times being accomplished asynchronously, though many racecar drivers drive in this manner and do so quite successfully. In fact, it is necessary to get the best performance out of their cars by driving in this manner. By contrast, when using two opposing fingers to pull the trigger, the fingers are performing the same task on the same mechanism at the same time in a mirror fashion.
3) Brain works best sending orders to fewer muscles
Okay, explain. How is it that the brain is working better sending orders to fewer muscles and is the difference significant?
Given that sympathic reflex often results in one hand mirroring the actions of the other, such as with squeezing actions under stress, I don't see how sending the same signal to both fingers to pull the trigger is going to be a problem.
So is it easier to stand balanced on one foot using half the muscles and supposedly allowing the brain to work best or is it best to stand balanced on two feet, using twice as many muscles and taxing the brain so much more?
I know a lot of shooters find it much easier to shoot well using a twohanded grip on their guns instead of onehanded. Controlling double the muscles does not seem to be a detriment to them at all.
Remember that in stressful times, fine motor skills deminish.
Right, and because fine motor skills diminish, the fine balance of trigger pull/squeeze/depression being performed assymetrically by one finger is going to be much more difficult to keep balanced under stress given that the balanced pull is being attempted through an asymmetric process of using one finger on one side. The balance is more easily controlled when the input to move the trigger is symmetrical. And that is likely why TXAZ's groups are tighter when he is using opposing fingers simultaneously to pull the trigger. Balance is more easily attained through bilateral symmetric action than by unilateral assymetric action.
If the only reason you shoot is self defence, too many things could go wrong while you are trying to stuff your second finger into the trigger guard, so you should fix it.
Right. Most guns are not designed in such a manner to allow for sufficient room inside the trigger guard for more than one finger with sufficient extra space for proper motion and placement. The more things stuffed inside the trigger guard, the more likely the trigger will be depressed unintentionally. This will be especially apparent in winter when you have on gloves.
The problem of trying to fit multiple fingers inside the trigger guard can become even more problematic if you are needing to use your offhand to perform other tasks and transitioning between gripping your gun with the finger inside the trigger guard and doing things like opening doors, fending off blows, doing magazine changes and the like.
Using multiple fingers can be advantageous in certain circumstances but does add a level of complexity to the issue that has the potential to affect safety.