That would have been great!
Okay, which one of you is Eric Stoltz? 
Both of those are pretty much why Stoltz decided he was in a tragedy.
Of course now that I think of it, he’s looking at it funny because the last time he saw it, Dave’s hair was missing (the timeline changes had already begun).
Marty’s reactions might not be accurate, but Morty’s seem pretty spot on.
Yet, note, despite subjecting M[o]rty to literally everything else, Rick wisely keeps the time-travel stuff boxed up in the garage…
Marty should have been the oldest kid, not the youngest, because otherwise when he got BTTF his brother should suddenly be Marty and he would be Dave (or Billy…).
Man this franchise really could be a total downer with just a slight change in tone.
Marty: Look Jennifer, this is the flyer you signed. See! ‘I love you Marty!’ it’s right there!"
Jennipher: “Why would I write ‘I love you’ to your brother? What’s WRONG with you? Maybe we should stop seeing each other, Dave.”
Well, Karl Marx did say “History repeats itself, first as tragedy, second as farce.”
And the third time with cowboys.
As far as I’m concerned, Doc merits a Special Award For Services To Filmdom if he can somehow keep that movie from being greenlit.
I think Marty was the youngest because there was still hope for him. He hadn’t gotten dragged down yet like his parents or his older siblings. If he hadn’t gone back in time, he would have wound up like them.
I don’t understand this rather common criticism of the movie. Many people look similar. By the time Marty was 17, thirty years had passed since another guy named Calvin Klein spent a week in their high school and presumably no pictures were taken.
Even if they remembered “Calvin” and thought that Marty resembled him, wouldn’t they remark off-handedly that he sort of looks like that dude from back in high school instead of concluding that their son was a time traveler? The former seems far more likely.
ISTR a Robot Chicken sketch where his dad confronts his mother about how much their son resembles that guy she briefly had a thing with back in high school.
I thought of Marty McFly’s situation as the plot in a great movie fantasy and gave it no more context than that. 
Especially since Marty looks like George, too (Marty is George’s son, after all). Lorraine has a type, that’s all…
I think he looks more like Seamus.
I’ve never had a problem with the idea of “another Marty.” The way time travel seems to work in that universe is that the other timeline stops existing, but only after a delay. That’s why Marty will eventually stop existing if he doesn’t get his parents back together. The change only happens gradually, i.e. Marty fading.
So, rather than there being another Marty, Marty’s past would just gradually change.
And, yes, I assume that going back in time is a fixed point. If Marty doesn’t go back in time, then his dad never punches Biff. That would completely change Marty’s past back to the original. Since that doesn’t happen, I conclude that even in the updated 1985, Marty still went back to 1955 and had basically the same adventure.
I hope that all made sense. It can be hard to talk about timey-wimey stuff.
Also, it’s not like Marty just showed up one day in 1985. They’ve seen him since he was a baby.
Not a bad theory.
I believe that when Marty time traveled, he created a brand new timeline, simply by his arrival alone. The old past, everything we saw in the beginning of the movie? Gone. Never existed. If Marty did nothing else with the rest of his life it would still be a different timeline. But he didn’t.
Therefore, Marty (and Doc) are the biggest mass-murders in history. Because of the timeline changes, people will be born (and died) who would never have been born, people will not be born who were once born.
But don’t worry. Other Marty (the one we saw time travel at the end of the film) will do the same thing, Everything we saw in the movie? Gone. Never existed. We the audience only got to see it before it went poof.
What happened in that world? Who knows. One assumes Doc actually gave Marty extra plutonium, so he doesn’t have to rely on the lighting bolt (or Doc would have to be more careful - the ledge is already broken!) Maybe there are TWO Martys and two DeLoreans in 1955. That would be a movie!
But Marty would have to deal with the knowledge he destroyed entire civilizations not yet born. Now that’s a burden.
I know deconstructions like this are fun, but I’m not sure that’s correct. The way they act seems to indicate that the butterfly effect isn’t true in their world, and you only really affect those you directly interact with. And we know at least that it didn’t change the existence of any of Marty’s siblings, so I wouldn’t be so sure it erased anyone else. It just changed them.
That said, even if he did wind up causing people to not exist, I’d argue that this is nothing special to time travel. If actions in the past can change the present (or future), then actions in the present change the future. You’re still altering the timeline with every choice you make, even without time travel. There’s nothing special about having already experienced a particular timeline that makes it more real.
Well, at least, there wouldn’t be under normal rules. But since the whole fading and time line intertia concept doesn’t really make a lot of sense, who knows how it works in the BttF universe. So I won’t take away your fun. 
I was kind of proposing that only as to how it might affect Marty. Carrying the weight of millions of unborn and never-born might be considered “heavy”.
I got to thinking about the “reality” of changed timelines in ST:TNG Tapestry (which I hate BTW), where Q alters Picard’s past such that his last 30(?) years are totally different. But that means that everyone’s life that Picard influenced, even second hand, has changed. If the butterfly effect was a factor, then that means entire lives were altered by Q’s one minor act of meddling. People were born, lived out their entire lived and died during that episode. And when Q reset things back to where they were, what happened to all those other people? Did their lives mean nothing?
If one believes in souls, did these people have them? What happened to them? Since at least for a while, these people were living out their daily lives, with all the pain and joy and heartbreak and success. And then it never happened. Just like that. That really bugged me, I thought, I’d hate to be one of those people. I could be right now, just a pawn in some Q’s little game, thirty years in the future, and I’ll never know when I am poofed out of existence.