One thing I’ve come to realize in writing the Ben & Sue thing is that, in general, it would be nearly impossible for a time traveler to change the past. I mean, think of the past like a vast river that you, one tablespoon of water, is somehow going to launch yourself out of and deposit yourself way upstream. Now, it is true that, in times of crisis, like a flood, it must come down to a tablespoon of water, eventually, being the difference between the levee being breached and it not. But that you are going to be that tablespoon at that moment? Highly unlikely.
The fantasy that you can change the past must, in general, be borne by people who feel they can change their own present.
But changing the past would, actually, be difficult. Who would believe you? Even if they did believe you, why would they act on it? I mean, we get told all the time by people who know what they’re talking about that global warming is happening and that it’s going to add to our own future misery and we don’t do shit. Why would we act on the future needs of people we aren’t ever going to be or know? Plus, the things you know about are very limited. So, what permanent change are you capable of making? Say you even know how to do something complicated–like build a computer–where, in the past, are you going to find workable parts? Okay, say you even find workable parts, where are you, stranger in a strange land, going to find another person with your talent to pass this knowledge on to in a useable form?
It’s hard enough, in the present, to intersect with the right people at the right time in order to move your life how you want it to go. And you know people here.
Which is not to say that it’s not possible for people to make change. Just that time travel to the past seems to unquestioningly rely on the danger of fucking things up for everybody, when, really, the odds of you being able to make any changes, positive or negative, are not good.