Did Marty and Doc actually mess up Marty's family's future?
I'm repost what I just found on AVClub:
https://film.avclub.com/1846511189share
The whole of the first film is about making sure everything happens exactly as it should so that it doesn’t wipe Marty and his siblings from the timeline (the couple of tweaks that improve their lives later is a bonus). But in Part II they deliberately change what happens in 2015 just because its a bit shitty (despite Doc’s whole “Don’t fuck with time, you’ll fuck it all up, oh great now Biff’s in charge and we’ve got alternate timelines” message with the almanac)
But what about Mary’s grandkids? And his great grandkids? By messing about with Marty Jr. and changing what happens to him and the effects it has on Marty’s other kids, surely they’re creating an alternate timeline? One where, whatever children they would have had, are now wiped out because circumstances are completely different? And their children and their children...
Basically the entire future McFly family born after 2015 are wiped out just because Marty didn’t want Marty Jr. to do a bit of jail time. I realize Zemeckis and Gale were somewhat trapped by their ending to BTTF (which was supposed to be a punchline, not a sequel set-up) but it’s funny to think the solution was McFly genocide.