“Tilda Swinton’s Ancient One and Mark Ruffalo’s Hulk establish the importance of not altering the past, so alternate timelines are not created.[…] All the time travel nonsense would have actually been completely fine if Endgame hadn’t stressed how any alterations of the past would create new timelines, and that this was an unequivocally bad thing.”
Well, I don’t think the movie says that creating new timelines is an unequivocally bad thing. I think that rooftop scene did a poor job of explaining the Ancient One’s objection, which has led to a lot of viewers misinterpreting her goals.
It’s not that branching timelines should be avoided altogether. They can’t be. Each of their travels back to the past would have likely caused multiple branching timelines.
I think the Ancient One was trying to avoid one very specific branching timeline, where they no longer had the time stone. Because not having the time stone would have led to a really bad future. But other branching timelines where she retains possession of the stone, those are fine. Or potentially fine.
“You don’t need to be Stephen Hawking to figure out the problems of the Avengers killing the Thanos of five years earlier — before he managed to get his big purple hands on the Infinity Stones at all. It means, of course, that the first Snap never happened at all, because Thanos died before he could do it.”
No, they specifically addressed this. Someone suggested going back in time and killing baby Thanos, and Hulk explained that it wouldn’t work. That time travel doesn’t work like in Back to the Future.
If you go back in time and change the past, you’re not changing YOUR past. You’re altering the course of events for the other you. But your own past remains unchanged. And so does your present, whenever you get back to it.
“We don’t even need to worry about how Loki’s freedom would affect the events of the second and third Thor movies, because now the trickster god has his own Infinity Stone.”
It wouldn’t affect the events of the second and third Thor movies at all, since changing the past only creates a new alternate future. The prime timeline remains unchanged.
There is a version of Loki out there who has an Infinity Stone, and that could mean some very bad things for that particular timeline. But it won’t change the prime timeline at all.
As for what that other version of Loki ends up doing with the stone, that might end up being what Loki’s new Disney+ TV series is about.
“But even this bizarre choice pales in comparison to keep that five-year gap. […] It’s such a weird decision, and so unnecessary — especially when the Avengers ended up having zero problems wrecking the timeline in countless other ways. Why not have them erase the Snap as well?”
Tony was pretty clear about what his reasons for that were. Undoing the snap would mean his daughter ceases to exist. He’s willing to try and bring everyone back, but he isn’t willing to help them undo the snap.
Of course, you could ask: Well, why did they write it that way? The writers could have just not given Tony a daughter, and then they could have undone the snap. So why didn’t they write it like that?
And my guess is, thematic reasons. Undoing the snap would mean Black Widow would have been brought back to life, and it might mean that Tony would have lived, too.
But then that would have felt like a cop out ending. You can’t have everyone survive. Some major character had to die, or the ending would have felt cheap and unearned. So they wrote in Tony’s daughter as a plot device for why he wouldn’t agree to undoing the snap.