>>92688850>>92688995Marty's time-traveling affected his loved ones as well as him personally. He didn't have a reason to worry about long-term implications for the world when he had much more immediate concerns, like the danger of vanishing out of existence. Even though he did erase alternate timelines, it's forgiven because it ended up improving the lives of everyone we saw (except Biff).
Samurai Jack's scale was wider. It was about trying to save the entire world, and most of the series took place very long after Jack's original era. When Jack went back in time to defeat Aku, it was unknown how it would've affected the future or all the characters he had befriended in that era.
Back to the Future has its own time-travel problems. Since Marty messed with the way his parents met, it should've altered the relationship of his parents enough to cause a butterfly effect that would very likely replace Marty and his siblings with some totally other kids. However, the movie confirmed that Marty and his siblings still continued to exist, so people just tend to accept that. But Samurai Jack didn't show on-screen that Scotsman and the others are still alright in the altered future, and that's why we're arguing about whether that's the case or not.
