You can go into your controller settings and custom map any of the functions. If you want to remove anything but aiming from the right stick you just need to unbind the other actions tied to it, which by default is melee. Like others mentioned, I mapped my push down of the right stick to go into a crouch so I dont have to move my hand off the stick to do combat moves. Melee action is generally much less frequent than all the shooting and stances, so I mapped that to B and to the right bumper. If you are on a computer using a controller you can also map keyboard buttons to your controller buttons for some more diversity in your control settings.