A while back I was watching an episode of Terminator: The Sarah Connor Chronicles. One of the characters made the claim that Kyle Reese would have been better off going back much further in time and killing Alan Turing instead of bothering to defend Sarah Connor to ensure John Connor would make it into the future to fight the machines. Presumably the argument is that without Alan Turing the project of artificial intelligence would have been delayed significantly.
Of course, someone else would have come along to do the kinds of things Turing did, so I doubt this would change too much, perhaps slowing down the age of the machines by a little bit. But there are two much worse problems with this suggestion.
First, there's an ethical problem. Turing is innocent. The machines easily kill people who would threaten them in the future, but should humans sent back in time by John Connor become like the machines in their willingness to kill any innocent that would improve things for the humans fighting against the machines?
Second, I can't imagine how this is supposed to make Reese better off (or help fulfill his mission any better). He was sent by John Connor to protect his mother from the Terminator, and in the process he became John Connor's father, thus not only protecting Connor but ensuring his existence. If he went back to Alan Turing's time, he wouldn't become Connor's father. Even apart from the metaphysical problem (he couldn't go back to Turing's time, because then Connor couldn't have been around to send him there), there's the mission issue. The basic assumption of Reese's mission is that if John Connor never exists we'd never get the resistance movement going. This mission prevents Connor's existence. So whenever the machines get around to trying to take over the world, even if it's delayed, there would be no John Connor to lead the resistance. Reese would automatically fail in his particular mission if he'd gone back to kill Turing instead.
Other than the silly view of time travel this show assumes (along with all Terminator movies except the first one), I really have enjoyed it so far (I have several episodes left to go in the second and final season). But this particular suggestion struck me as being just stupid, even if you suspend disbelief and go with the crazy view of time travel they presuppose.