You're correct to put a positive spin on the fact that we care enough to protest, Jim, but I feel you're being unfair in the way you describe everything else.
I wouldn't say that the fan response to the ending has been unreasonable or childish. It has included a charity drive that has raised over $70,000 for Child's Play so far. Furthermore, the reasoning behind not accepting the ending(s) had nothing to do with a lack of respect for Bioware's artistic integrity. Fans don't deny their right to write their own ending to the story they began. It's not about satisfying demands that we have cooked up in our own minds... It's about being consistent with what they made the series and its central character to be up to the very last moments. Even a twist ending has to share the same universe and be logically consistent with what has happened in the lead-up to it. ME3's ending(s) failed in this regard. The ending(s) did not make sense in terms of the lore of the universe or in terms of Shepard's character.
The narrative flow of the entire game had been leading us to certain conclusions when it came to, for instance, the possibility of cooperation between synthetics and organics. Why introduce a totally new character in the last moments to contradict this? Why have Shepard blandly agree, with no possibility to even protest, even though s/he has been able to protest every single instance of similar arguments from any other character up to this point and has no reason whatsoever to trust this new figure that just appeared? It's not a brave storytelling decision that we can't understand only because we're not making the effort or we're not smart enough. It's terrible writing. It makes no sense. It does not give any satisfaction or closure. Neither do the differently-coloured cutscenes that play out afterwards.
I cannot think of a single reason why Bioware would have found it in any way satisfying to write what they did. (I know I certainly didn't find it satisfying to play.) But if you read their comments about it, it's almost as if they think they wrote an entirely different ending to the one they did. When they talk about what they didn't want to do, they describe exactly what they did. It defies understanding.
As fans, we expected better. Everything prior to the ending was so good, so emotionally powerful, and so well-written that to have that ending conclude it all is impossible to understand.
Given that the current situation with games is that they can continue to evolve post-release (and, in the case of Bioware's games, this has happened a lot in the past few years), I think we have the right to ask for an improvement to be delivered via DLC. I don't believe in "demanding" anything, but I don't think it's unreasonable to ask. That said, before I experienced the ending for myself, I would have thought it to be arrogant even to ask... I had felt hurt by the ending of Dragon Age: Origins, in which my character lost everything she really cared about, but it was superbly written, it made sense in the context of everything that had happened before, and I respected that Bioware had pulled off some stellar writing in making me feel so much pain. I would never have imagined that a time would come when I'd ask them to change an ending they'd written. Now, though, I do understand. Now I think that for Bioware to fail to improve the ending(s) of Mass Effect 3 would be to leave unrepaired some fatal damage to their intellectual property, to their brand identity, and to their trust with fans. It can only benefit everyone for them to admit a mistake was made and to write something better. I know they can. They put so much good material into everything but the ending that they have to be able to do something better.