Very interesting and I look forward to the next part. As for my thoughts.
Politics
This often makes the excuse round not from people with legitimate concerns, but people that would take up the big brother role and censor differing opinions if they had the chance. Most of the movie going public isn't overly concerned about the politics of a film going in. Avtar was very one dimensionaly left leaning, but it did big numbers, so big it's more likely that a lot of people put their normal inclinations to see half naked blue people in 3D. To balance it out, Starship Troopers had a one dimension pro military message I don't agree with, but I still enjoy watching the film when I'm in the mood for big bloody war action. Yeah, others find the political views they want to see. V faced not a generic big brother government, but a Bush inspired government to many people because they want to see that view (I won't get into why for fear of offending anyone, but it's safe to say that at that point, people are just looking for things to complain about.)
Boys
We talk a big game about wanting deeper films for adults, then turn Transformers 2 into a blockbuster and pretend the one dimensional philosophy lesson in the Matrix is the deepest thing around while missing the point entirley. Face ti, we're a stupid people that like to pretend we're not. Transformers 2 did how many hundreds of millions? That's a lot of teenage allownaces. We have to shoulder some of the blame for that. The fact is they are marketing to us, and we don't like what that implies. As for Tiwlight, it's a cheap romance novel pandering to basic urges. It's the female equivilant of an American Pie movie.
Originality
You know I have surprised people by telling the the Wizard of Oz was a book first (heck a series). Adaptation and sequals are stock in trade, and that isn't a bad thing. Then the nostalgia glasses set in and we forget that the stuff in MST3K was very real, and probably more representive of the average film that those chosen to be preserved. The reality is we've been oversaturated. You said about Kinght and Day that it was probably a movie you'd enjoy if you didn't see this kind of film as often as you do. That effect has hit society hard with mega cinemas, pay per view, cable, satelite, and downloads, not to mention books, TV, video games, anime,, I could go on. The reality is we've been oversaturated with fiction to the point where it is hard to impress because we've seen so much. It's no longer a treat, it's 3 meals a day. It's not like they're all bad, but we're more likely to have seen it before in some form and therefore get bored, and unfortunatly, innovation and origianlity is a lot harder to deliver on than to ask for. Then point 2 comes back to haunt s as when something unique does come along, we're too afraid to give it a try and fall back on old favorites.
Man so much of me expects one of the reasons you think movies suck today is that we are dumb enough to keep shelling out for the tripe they feed us.