People here tend to forget that being dissatisfied with a product or service is your God given right. If you are unhappy with something, you will demand getting something, the value of which you paid your hard earned money for, as compensation.
If I buy a lawnmower, that cuts the grass perfectly, but ultimately burns whats left of the grass in my yard, when I was promised by the manufacturer it won't, I will not take it just because it was the designing teams artistic vision that all grass should be burned. I will demand something be done with it.
If I go eat at a dinner, order for the double sized burger and come up with a thin slice of bacon between two buns, I will not take flak for arguing with the cook over his artistic vision over what a double sized burger should be. He will cook me a new one that corresponds to what was promised to me and what I paid for.
If I go to a movie theater and did not enjoy the movie I watched, I can, after the movie's end, ask for a refund for a product I did not enjoy and had no control over. I will not have to argue with the movie's director over his crappy sense of artistic vision.
In cases of some movies, I think it happened with 'The Devil's Own', the entire ending was changed after a test screening showed that if Harrison Ford shot Brad Pitt, people would not like or go see the movie, which was the movie's original ending. It's not what the audience signed on for. Would there be people that would have liked to see Brad Pitt get shot by Harrison Ford? Yes! I would like to see it, because I don't particularly like Brad Pitt and would enjoy the heck out of seeing Han Solo shoot that pretty boy. The new endings works just as well, if not better, and more people got what they wanted.
The thing with ME3 is that you sign up for both a product and an online service. Its main goal is to appeal to the masses. Most of the game is very entertaining, despite being heavily bugged and everything seems to come together, except the lazy ending. 1 frigging cutscene that shows the exact same thing, regardless of choice, but with a different color. We demand to be shown substantial differentiation between the endings.That's what we were promised, that's not what we got.
People that are upset over the endings, do not want to send the game for a refund because they actually are happy with the overall gaming experience they got, minus the endings. They like the game and they would like to keep it, but they will, if they continue to be dissatisfied with the product. And that would be much, much worse for everyone involved. What they want is for BioWare to keep their promise. Regardless of whether you like the ending or not, you have to agree that the promises that were made, were not kept. This is non negotiable.
If you are OK with BioWare doing this, then you are basically telling each and every developer/publisher that it is OK for them to blatantly lie to you and mislead you about their products, in order to maximize their profits at the expense of your finance, entertainment and invested time. This is what we're fighting for. We're not fighting just for us, we're not fighting just for ME3, we're doing this for the sake of every game to be made and we're doing this for you, who actually liked the ending, so that next time, when it does affect you, you won't have to go through this, just like we did.