Back to the Future Part 2: What was the point of going to the future?

Question

In Back to the Future Part 2, Doc practically forces Marty to come back with him to 2015 to correct something regarding his kids. Basically Marty Jr. needs to say "no" to Griff so that he doesn't get jailed. So Marty Senior does his task, gets Griff's gang jailed and his son Marty Jr is free and will not go to jail. Task completed. Go back to 1985 and everything will be just as it was at the end of Part 1. Biff owns a car waxing company; George McFly is a successful author.

Here's what I don't get : What exactly is the point of going to the future and correcting it, and then coming back to the present? You're still going to have to live through it again after you arrive in 1985. It would have made sense if Marty and Doc were planning to live in 2015 permanently (a hard task given that their future selves will be milling about). But just because Marty Jr avoided jail in the timeline featured in the movie doesn't mean he won't once again get the same request by Griff to take part in a robbery through the natural progression of time. (when Marty returns to 1985 and lives out his live the normal way). Marty Jr is once again going to have to say "no", once again get chased on hoverboards, beaten up etc. And who knows if he'll be successful the 2nd time around?

Answer 1

I think the most simple answer is that this is what the characters did at the end of the original film.

Bob's Zemekis and Gale never had any intention of producing a sequel and never originally considered crossing that bridge story wise - even the famous pre- credit 'To be continued...' frame was only added as a joke to the original home video releases.

When it came down to actually designing the story for Back To The Future Part 2 the Bob's quickly admit that if they had actually intended to continue the adventure from the get go they would not have placed Jennifer in the car due to the paradox potentials her presence would create, hence they knock her out almost instantly upon arriving in 2015 and drop her completely from the story at the first real opportunity...

(All of this information is presented on the Back To The Future Part 2 BD from Universal Pictures)

Answer 2

It's not the worst plan ever.

Firstly, the Marty of 1985 is arguably more grounded than his 2015 self.

Although there are plenty of ways that Marty could just try to keep his son from getting involved with Griff, the Doc might have not got great faith in Marty's parenting abilities given what a "Loser" he has become. Besides, he would have to explain the whole thing to Marty and he believes no one should know too much about their own future.

Since Marty looks exactly like Marty Jr. of the same age, it should just be a quick stop-off at the Café 80s, say "No", then leave - Marty would have minimal exposure to the future. Doc didn't know that Marty Jr. would wake up and interfere with the plan, or that Marty would buy the Almanac (and give Biff the idea to steal the time machine), or that Jennifer would get taken home by the police - so it should have been all OK.

Now just on your statement that he would have no guarantee the second time around - technically you are correct because the new period of 1985-2015 is slightly different in that Marty knows what he's done. But if we ignore the so-called "butterfly effect" of this minor change (which is not unreasonable for "movie logic"), then we can assume that everything will go exactly as it did in the first version of the time-line, because - why wouldn't it?

It's not like the old joke of the footballer scoring the penalty kick but missing the replay... this is the timeline, and the change mentioned above aside, everything would proceed exactly in a specific way whether or not someone traveled to the future to check whether it did.

(The Doc reinforces this point when he watches Marty Jr. through the binoculars and says...

Precisely on schedule!