Not everything is going to be fixed by time travel. Jacob isn't Horace and Amy's baby, who travelled back in time and ruled over the Others so by 1954 Richard would recognise his name when Locke showed up. But what if some things can be fixed, or at least changed? Or can they?
Daniel insists that the past cannot be changed, and whatever happened, happened. Is Daniel self-delusional? Is he afraid of a change he knows he is supposed to make because he worries about the butterfly effect?
The past has already been changed to some extent just by the presence of our merry band of time traveling, now-DHARMA-uniform-wearing Losties and Science folk in the past. Even if you subscribe to the "they were meant to be there so it's not really changing the past", you cannot deny that changes were made in the past by people from the present.
Amy is nearly kidnapped after Paul is shot, until Sawyer and Juliet step in to save the day and kill two Others. Past is changed. If Juliet and Sawyer were not there, Amy would not be saved, and the two Others would not have died at Juliet and Sawyer's hand. They might have died that day by another means, and Amy might still have escaped kidnapping, but it is straight fact that change has occurred as far as Juliet and Sawyer's involvement.
Horace is drunk and blowing up trees, passed out when Sawyer and Miles go to get him. Horace might have stumbled home in the morning, still saddened he missed the birth of his son, but the past, again, was changed. It's not "stepping off the path and squishing a bug which results in the instillation of a dictator" change, but it's still change that Sawyer carried Horace home and Miles cleaned up, thereby saving Horace's reputation. Who knows what would have happened had they not been there, since we do not see the alternate timeline.
Most importantly, Juliet saved Amy and Horace's son in the emergency delivery. Would he have died? From the clues we are given, it's almost assured. They couldn't get her to the mainland in time with the sub not yet returned. The baby was breech, and the standing doctor was so incompetent as to not have attempted the turn before it was too late to try. Juliet did an emergency c-section, and the baby lived.
In the Dharma booth video, Chang loses the plot and begins to heartily plead for change, to have the viewers of the transmission from the present continue the experiments and save the people of the past. That would be change.
So. Is Daniel correct? Can the past not be changed? Is Chang correct and it can be changed?
What is change? And how much change nullifies "what happened, happened"?
Or is it all an exercise in course correction, where going to the past is actually fixing events for the present to play out properly, as it was intended? Where's Sam Beckett and Al Calavicci when you need them most?