Take your firing hand and grasp your other forearm with pressure comparable to your firing grip. Now wiggle your index finger while maintaining the same amount of pressure with the other fingers. Now do the same thing but wiggle your middle finger. Notice the difference? Your index finger can be moved independently while your middle finger can't. Since it's impossible to get consistent hits without good trigger control, which finger do you think is better suited to the task? Obviously, if someone lost their index finger, they would have to make the best of the situation but using the middle finger is the answer to a problem that doesn't exist.
ps. point shooting doesn't dictate that you use your middle finger. It's just shooting without visually verifying that the sights are aligned. I suggest you take Jeff's advice and find competent training before you get totally messed up.