1) It also boils down to your average adult not having the time or energy to produce a viable solution. Again, you want to talk about your ability to prevent conflict. You're 18 years old and decide to spend your life curing cancer, in case you or your loved ones contracts the disease. Instead, your loved one comes down with a completely different disease you weren't expecting. Solve this conflict, feasibly. It's utterly impossible for one tragedy. Now tack on infinite more on top.
Yet there was nothing that prevented you from making different decisions that, if you had known differently, means you could've got better results. Replaying a game though is doing just that. If it's possible I'd like the game to avoid being too hardcoded to be able to do that sort of metagaming (if your example was a game it might choose a random disease every time), but that's hard to pull off convincingly, depending upon the situation. However why then say "We're forcing you to be wrong"?
2) You can't metagame life, so your point fails. In ME2, you meet Thane after diagnosed with a deadly disease, having only one year to live. If you want to play a Shepard who spends his mission curing Thane, go for it. But you're also playing Shepard who isn't solving about a million and one other, higher priority conflicts. All conflicts cannot be simultaneously prevented without also generating (or neglecting) other conflicts. I'm not sure if you actually think such a thing is possible.
No, my point doesn't fail. If it did it would mean that you could only ever have one playthrough of a game.
The Thane example is a constraint due to the starting point of the game; the starting conditions impose some limitations for sure, but that's a world away from defending events that aren't inevitable for those conditions.
What evidence do you have that preventing one conflict just means you'll get another? History is full of conflicts that didn't happen, it's usually just hard to identify them. The fact that a lot did happen too doesn't mean that it was always one or the other.
3) Morally ambiguous as in, no perfect outcomes where the player gets everything. It does not mean the player will not prefer one solution to another. Clearly the topic is worthy of intellectual consideration. People have debated this exact topic since Ancient Greece, to the point of writing books, films, and even games where it's the focus.
Are you seriosuly trying to suggest that it's morally ambiguous or perfect?
4) No, I'm simply pointing out the foolishness of your statements. The goal is to provide the player with a probable set of responses to a given situation. Simply saying "herp derp, go back in time!" isn't a solution. As Alan pointed out, you're not playing a sandbox. The game is only going to provide so many responses to a given situation. The only way your solution works (if at all) is for the game to allow the player access to extremely absurd actions or ideas, which don't work within the context of the narrative.
Perfect example: ME1, I can't play an omniscient Shepard who magically realizes on the Normandy that he needs to search the Mars Archive for Crucible plans which he doesn't even know exist yet. But that could theoretically meet your criteria of preventing all of ME1's subsequent tragedies. If that's the sort of solution Bioware needs to implement, I think the story is improved as a whole without their existence.
I seriously hope you didn't think I meant literally going back in time. If you did, and called my position "foolish"... Replaying the game though is essentially going back in time. Why should events have to turn out the same way?
Yes, a probable set. Most of the tragedy resolves in only taking a certain subset of those probable outcomes and just keeping those which give the tragedy the writers want. Even some improbable ones should be there every now and then, to cover equally improbable behaviour by the player (either unbelievably good or unbelievably bad), although clearly it's not worth putting too many resources in to those. Arrival had one for example, the clock could run down, although you need to be a pretty awful player for that to happen without deliberately letting it.
Why aren't I playing a sandbox? Is it for any reason other than it's impossible to get the depth for an engaging story and characters out of a sandbox, so numerous tradeoffs against player freedom have been made?
Your Mars Archives example illustrates my point - Shepard could've gone to Mars and found the plans. It is a possibility. A very remote one and therefore justifiable in leaving it out but that's not the same as saying "Couldn't ever happen."
6) I am completely aware of its strength, hence my Heavy Rain comparisons. I have purposely pointed out that this is not a game's only ability. Hence why I've stated that, just as a game doesn't always need to have good and bad outcomes, it doesn't always need morally ambiguous. The point was that morally ambiguous scenarios have certain advantages completely denied by the existence of good outcomes. The gaming medium can make players feel powerless just as it makes them feel powerful. Games like Half-Life 2 have done this very well and are extremely well-received.
OK, you're playing a game and have wound up in a situation where you've got to decide between "Not great solution A" and "Not great solution B". You're implying that that becomes worthless if you could've made a different decision about something else earlier in the game to avoid getting into the place you're in now. The simple fact is that you made the earlier choice you did, you're in that place now, you need to think about the choice you're facing now. I don't see how the fact that an unambiguously good outcome might've happened if earlier events had been different denies anything about the current choice.
The point you mentioned earlier about probabilities might mean that the chance of making the right choice earlier without metagaming would be so remote as to not be worth implementing of course, although you still need to be very careful about the specifics of the outcomes of what choices you do have if you don't want to get accused of contriving events.