If Jack had helped young Ben, he wouldn't have gone to the Others to become who he is today.
Not necessarily. If Jack had agreed to helped with Ben then the timeline would have self-corrected and events would have still played out more or less the same.
Example: Jack agrees to help, but on the way to the infirmary he trips on a rock, smacks his head on (insert random object) and is knocked unconscious for a long period of time. Events play out the same as if he had not agreed to help.
Not the best example, but you get the point. Jack is not to blame. Sayid is not to blame. Whatever happened, happened.