Exactly! There's just no conceivable mechanism for travelling back in time that we can come up with which passes even a basic sniff test. "Something something wormhole" is literally the most plausible method we've got.
OK. So let's knock together a wormhole.
As insanely difficult as that might be, it still might be the easy part.
What are you assuming will happen if you go back and change the past?
I'll save the world?
OK. But if the world was saved, would you still go back in time to save it?
You're talking about paradoxes.
Yeah. That's the classic problem with time travel: Either it's logically impossible, or results in all of reality exploding into stopwatches or something. There is one possible way around that, whereby in traveling back in the past and changing it, you end up in an alternate universe. But that just means the new universe you're in is good, while the crappy one you just left remains doomed.
Yeah. Nice work, idiot.
Another unsatisfying solution to the paradox issue is that you might travel back into the past and find that you can't change anything at all. Maybe it's because everyone ignores your prophecies, like some modern-day Cassandra. Or maybe it's just that everything you do only reinforces the event you're trying to stop.