>>62235012Every single element. There isn't a single thing the movie gets right, from the absolute basics like Marty interacting with anything creating a butterfly effect that would destroy the universe, the lazy handling of paradoxes as something that might be bad in a couple of weeks instead of literal world ending death. Even if you've got a hard-on for time propagation, that gives you either 30 years until everything explodes or a couple of minutes, not a few weeks of playing with your dad while you try and fix a time machine.
The Biff event alone would have had massive consequences that would ensure that Marty's dad never even had Marty, because he'd be jerking off less that week or some shit. Not a single element of the time travel makes any sense unless you're stupid and take everything at face value.
For example, T1 is a perfect time travel movie, as long as you ignore the delusions of Reese, assuming that he's simply been misled by Connor to give his best. In T2, everything falls apart, time travel wise.
