Why does Congress have such a low approval rating?

I have often pondered over the years why politics is so messed up. I mean, why is it that politicians can’t seem to just get the things done that people want them to get done?

For example, congress’s approval rating is something like 25% right now, several points lower than President Bush’s approval rating. Is it really that hard to do your job so that more that a quarter of Americans approve? It seems like you should be able to get a 50% rating relatively easily.

Some possible answers I have considered for why the national legislature is so widely disliked:
1.) Power has a tendency to corrupt. Many of these powerful men and women have been caught using their power in a corrupt manner.

2.) The American culture is not as homogenous as I have a tendency to think. Maybe there are so many different views on how the national government should act that congress can not please all or even most Americans. Each segment wants something that is contradictory to the wants of the other segments.

3.) Members of congress have a tendency to “play politics” too much. Instead of spending their time researching, writing and passing laws, they spend their time accusing other members of the government of no-nos. They propose laws or block passage of laws based on campaign contributions from lobbyists and not on the general good of Americans. They transparently and consistently hold members of their own party to a lower standard of morality and ethics than members of the opposing party.

This has been the extent of my pondering up until a little while ago. Though I think there is some truth to each of the above answers, I have recently become convinced that there is at least one more answer to the question.

4.) Americans don’t know what they want, so congress can’t give it to them. Or in other words, even at the individual level, many Americans want contradictory things.

I guess in some ways this is an extension of #2.
I first considered this one time when I was watching PBS and they were doing a report on a “town meeting” they (PBS) had conducted with some community college students about Social Security and what some solutions could be to the predicted shortfalls in the future. (This was way back in 2005.) Anyway the students almost universally were not interested in any solution that would give them less in benefits (or risk of less in benefits) or increase their contribution burden. There was only one student interviewed who said something to the effect of, “The status quo is unsustainable, therefore I see a reduction is benefits – such as indexing benefit increases to prices instead of wages – as one of the only reasonable solutions.”
When the concept first hit me hard was a few weeks ago when I was reading some columnists' reactions to Michael Moore’s “Sicko”. More than one columnist mentioned the finding of some survey that the majority of Americans want nationalized health care. In my mind I scoffed. I bet if they asked the same Americans if they would like their income taxes to increase by a few percentage points the majority would say no. Yet it is extremely likely we wouldn’t get the former without the latter.
As I started thinking about this more I realized that I am guilty of it too. I want the American government to concentrate their efforts on our numerous domestic problems. I also want America to do what it can to relieve suffering around the world. I want the low prices and competition that would accompany free trade agreements and repealing tariffs, but I also don’t want American workers to lose their jobs and livelihoods. You get the idea.
So I think that we Americans have a tendency not to approve of Congress’s actions while we fail to realize that the alternatives could have been just as bad or worse.

Actually, I think that having unrealistic expectations is a general problem in America, perhaps bred of continuous prosperity. We want to ask what our country (or insert spouse, company, school, community) can do for us instead of what we can do for our country.

This is still kind of a half baked thought, so tell me what you think.