They will, or they have?
Kayaker wrote: “They will, or they have?”
It all depends on your point of view.
What my point of view is, or was?
That’s one of the things I like about the NBC series, Timeless. The time-traveling characters have discussions over the ethics of what they’re doing, and argue over free will versus predestination. The female historian (whose sister was erased from existence as a result of their first time trip) argues that it’s their responsibility to preserve history, and that anything they change could have devastating effects on their own time; the male military officer argues that, even without time travel, every decision you make has effects on the future, and that they have the potential to make changes in the past that could change the present for the better, not just for the worse. She argues for preserving history; he argues for following his conscience; both seem to be slowly coming to appreciate the other’s point of view.
Bill & Ted had a fun time with it. “Ted! Remember to take your Dad’s keys!”
Up The Line was one of my fave time travel stories. Asimov also had a good time with effect-cause-effect problems in The End of Eternity
HHGttG showed how problematic time travel verb tenses can/have/will be become.
Wow, that’s a good point. It’s never occurred to me before.
But how does the time line work in which the 2015 Marty had a car accident in 1985? I can’t work out how any Marty gets to the intersection where he is called a chicken without knowing to let it go. As Quimby said, the only Marty that could have got there had already jumped into the future, and when he got back he already knew to take it easy.
(Sorry, this might be a hijack - probably not the right thread to go into BTTF timelines yet again. I’ll try searching old threads to see if it has been addressed.)
I don’t mind if the thread is hijacked, I’ve got some reading material. 
Plus, I was only wondering about some of the more mundane ethical issues with time-travel. Imagine if I could go back and save a couple of Honus Wagner cards or Action Comics #1? Or as I said in the OP snake someone’s lottery winnings?
Well, if you’d happened to find one of the Wagner cards or AC #1 issues that someone had thrown out (remember, baseball cards and comic books weren’t considered something you’d want to keep or save) then you’d wouldn’t be taking any money away from their owners.
But you’re devaluing the cards owned by other people by increasing the number in circulation.
I guess you could say that about most cards and comics from the 50’s, 60’s and later, but those two specific collectibles are so rare that the appearance of another one of each shouldn’t effect the value that much. Now, if you brought back several of each, then yeah, that could start to devalue them.
In that case…has anyone ever read/watched a time travel story where characters wonder about the ethics of changing the future instead of the past?
One that I forgot to mention until just now that touches on ethical issues–Time Travelers Never Die by Jack McDevitt
As long as we’re tossing titles out there, John Varley’s “Millenium” is pretty good.
I remember Simpsons episode where Homer goes back in time, changes something and returns, is horrified by the results, goes back in time again, changes something else and returns, is horrified by the results, goes back in time again …
Kinda what the OP is looking for.
A nice complicated time travel novel is “All of An Instant” by Richard Garfinkle The SF Site Featured Review: All of an Instant
I found a couple of brief essays on ethics of time travel you might enjoy perusing. Both reference some fiction, some of which was already mentioned here.
Ethical Considerations While Time Travelling Through Fiction
How about the ethics of being Ray Milland, The Man With X-Ray Eyes???
Larry Niven had a couple of thoughts on the matter. “Singularities Make Me Nervous” is about a time traveler who tries to do something unethical, and it backfires. “Rotating Cylinders and the Possibility of Global Causality Violation” is about two governments who attempt to use time travel as a weapon of war (it also backfires).
His stories about Hanville Svetz, collected in Rainbow Mars, deal more with metaphysics than ethics, but they are entertaining.
And Niven also wrote “On the Theory and Practice of Time Travel”
Another interesting work along these lines is the Spanish TV series “The Ministry of Time”. Quite recommendable!
Here you have some information: El ministerio del tiempo - Wikipedia
JoseB