Actually thats one of the biggest reasons I liked Terminator 1 much more then Terminator 2. I believe in the circular time theroy. It makes much more sense then messing the past. There is no way to alter events. A neverending loop is how I imagine Time travel works. You can't change to past. Destiny is the will of God and no time machine can change that. It has to happen because it already did. This principle is used in several Sci fi movies. Animorphs, Gargoyles, Timeline, and Kate and Leopold. Though the Terminator does it best. I personally think its more logical and probable then any past changing idea.