There is even the question of whether or not our interpretation of "time travel" makes any sense at all in terms of how physics actually work. I've seen suggestions in serious think pieces and reviews of scientific theory that suggest the concept of linear time may be tied directly to how our brains work, rather than how the universe works. If that has any truth to it, then messing with time is likely to have drastic unintended consequences.
That's the same kind of people who seriously believes that sending off one end of a wormhole at near FTL speed to cause time dilation for that end alone is going to make timetravel possible through the wormhole.
One sideeffect would also be that it would be literally impossible for actions to have consequences. Which means that our existence would be impossible.
Excusing their failure to comprehend what the math models they play around with actually MEANS, with "our brains can't understand it", is just epic fail and shows exactly why math=/=physics. The map can never BE the territory.
There were some really good points raised in the discussion. One thing I didn't see had to do with the morality of time travel. Is it moral to cause bad things to happen to undeserving people through the random changes caused by changing the past?
Unless you had the ability to reliably predict what the side effects of what you did would be, then how ever could you be morally responsible?
Anyone with even the slightest hint of intelligence understand that you do not drive while drunk, because the risk of causing accidents and injuries is simply so high that any time you did so you would have to accept that it was LIKELY that you would cause problems somehow.
But simply "driving a car" somewhere? The vast majority of cartrips does not cause any impact however, and as such you cannot expect it to happen, if it happens anyway but you did not in any way cause it, then how can it be morally bad?
In regards to timetravel, as long as you don't do anything that could predictably cause harm, well, noone can do more than that regardless of timetravelling or not. ANY timetravel WOULD cause changes no matter what, some good, some bad, but the thing here is, this would be the ONLY reality for everyone except the timetraveller(s), and it's utterly impossible to take responsibility for everything. Otherwise you're arguing that the only moral thing to do would be to do that every day as well.
Furthermore, if you can go to any point in a timeline, then is the timeline itself static? Varga in my fic is very much taking the approach of saying that only people outside of the timestream may be seriously screwed with by changes to it. In reality, though, if you can see the full timeline, and you change it at a point convenient to you, aren't you playing god with the lives downstream?
If it's possible to timetravel, then the timeline by default cannot be static. Or it could not "accomodate" for or "accept" the existence of the timetravelling people where they should not be.
IF timetravel is possible, then if someone travels back in time and changes something, to the traveller the time in between has already happened, but to everyone else, it will never happen. If this erases the timetraveller from the future, and he goes back to where he came from, everything is different, noone knows who he is, because from their point of view, he has never existed, while the traveller has absolutely no clue about the new timeline. The timetraveller moves outside of time, this keeps them from being affected by timeline changes.
It gets fun if you start looking at how multiple timetravellers going in both directions from various points in time, and how they affect everyone else depending on whether they have a radical impact or not in the time they go to.
