Mr Kenny:
To help clarify the reason why its necessary for pilots to have immediate and final authority to carry out a missed approach or 'go around' without first requesting permission from ATC, please consider the following:
A plane which is descending at 800 feet per minute, 300 feet above its touchdown point experiences sudden atmospheric change such as wind sheer, or a violent crosswind to the extent that the approach is too dangerous to carry out, and must be aborted. Lets assume this particular ATC is busy, the pilot may have to wait a few seconds or longer for the frequency to become free to request a go around. Then he has to request the go around and wait for a response. Then ATC informs him he is cleared to go around (or perhaps informs him he cant go around?!?). As you can see this takes time and could reasonably take 20 seconds or so for such a clearance.
Now if the plane is descending at 800 feet per minute, 300 feet above the runway when it becomes apparant that a safe landing isnt possible, it hardly makes any sense for the pilot to have to wait for a clearance to go around, when his plane is just moments away from slamming into the ground, does it? For this reason the necessary safety conditions are in place for any pilot on final approach to carry out a 'go around' at his own discretion.
Hope that helps clear things up!