In more detail, suppose there was in fact no conspiracy and Oswald was a lone, self-motivated individual. It might still turn out that the simplest way to imagine what would have happened if Oswald had not killed Kennedy, would be to imagine that there was in fact a conspiracy, and they found someone else, who did the job in the same way. That would arguably be the change which would minimize total forward and backward alterations to the timeline.

Hal: what you describe is called "backtracking" in the philosophical literature. It's not usually seen as legitimate, I think mostly because it doesn't correspond to what a sentence like "if X had occurred, then Y would have occurred" actually means in normal usage.

I mean, it's a really weird analysis that says "there really was no conspiracy, so if Oswald hadn't shot Kennedy, there would have been a conspiracy, and Kennedy would have been shot." :)