Here a few points @OP relevant to the discussion:
(1) The presence of optimal options in the subplots of a game is not a problem. Only the presence of one superior outcome overall is one. If there is a balance between situations where you can clearly win (Connor in DAO), hard choices and the (rare) situation where no matter what you do, it feels like a failure (Leandra's death), that's as it should be.
(2) As for the question: who would ever choose something else but the sunshine&rainbows outcome? Well, there are those of us who actually roleplay and make decisions appropriate for their characters regardless of the outcome. While I do consider a roleplaying approach to a Bioware game superior, it is not the developers' place - nor yours or mine - to educate other players on its superiorness.
(Example: in the ME3 replay with my main Shepard, I sent the biotic youths to the frontline, even knowing they would die. The thing is, my character didn't know, and he thought we couldn't afford to keep them back. To act like this, however, was my playstyle. I wouldn't force it on someone else).
(3) Even if you are roleplaying, you are also shaping a story, and doing so with advance knowledge and specific outcomes in mind is not an inferior appraoch to shaping a story than doing so blindly and accepting the unknown consequences of a decision. That's the mistake ME3 made: the writers wanted the story to be about the virtue of sacrifice, but for many players it just wasn't that kind of story and the sacrifice felt forced into the story for them. Storytelling is always a collaboration between the storytellers and the reader/listener/player, in a game even more so than in more linear stories. The writers present different paths, but it's up to the player what to do with them.
(4) You say you want to guide players towards acceptance of inferior outcomes. Well, the operational term here is "guide", not "force". Also, if the developers actually wanted to do that, it is far better done with in-world mechanics. One way would be to make the presence of the optimal option dependent on a decision made much earlier in the story, and let the player know that at the time when the options of the later decision appear. The player now has the option to replay from a few hours earlier, or to accept the consequence and go for the optimal outcome in a different playthrough. If you use in-world mechanics, the message sent to players is "this is a story and you made a supoptimal decision". If you break the fourth wall to do it and implement it on the level where you perceive the game as a piece of software, the message is "we, the developers, are telling you that you played wrong". I hope you can see why the latter might be considered offensive.
(5) Those who would dislike such a feature would just find a way around it. Actually, I would make it a point to publish ways around it even if this proposed mechanism never affected me. I find the mindset that might lead to such a feature insufferably patronizing. It is acceptable only in games with clear win/fail conditions that you tend to approach as a game rather than a story. For instance, in XCOM, if you reload an in-mission save (as opposed to a save in the XCOM base), you get a hidden -10 or -15 on the next attack. While I found that somewhat acceptable in this case, it still was occasionally annoying since crashes did happen. Meanwhile, the developers also accepted save scumming as a legitimate playstyle by *adding* a game option "reset the RNG after a reload" with the "Second Wave" DLC. No patronization here. Thank you, Firaxis. I'm saying this as a player who acknowledges that the "ironman" playstyle is the most authentic way to play this (!) game and who has completed games on Classic/Ironman.