Why the rage? You could do a little reading and find out for yourself.
Here are some ideas from me - some stats, some anecdotes.
1. Scientific output in the US is stagnant compared with China. For example, between 2010 and 2013 the US published approx, 560k articles each year. China rose from 335k to 426k. I often hear Americans say "Quality, not quantity." But again, no one had to say that 10 years ago... (see ref1)
2. The US standard of living has fallen below that of many other countries (see ref2). Again, many Americans deny this, or simply don't believe it. This is part of the problem. For example, this post (ref3) was rated 5:Insightful: "Government has a very limited range of things that they do as well or better than the public at large (war/defense, money, basic law enforcement, etc) - governmental action beyond that range invariably becomes incompetent, expensive, dangerous, or worse." Given that the poster is comparing Sweden with the US, this is laughable.
3. You can't put a person in space anymore.
4. You have people living on the street who aren't drug affected or mentally unstable. You know, like young, sane healthy families living out of their car. If you can't or won't fix that, you shouldn't have much confidence for larger problems.
5. Among the many Americans I've met (and they were all friendly decent people), there was a strong feeling that their country was the envy of the world. This is simply not the case. Here are two anecdotes that may have wider applicability. If you were to offer an academic the choice between a US or EU passport, what do you think they would choose? Among the people I know, about 3/4 would go with the EU passport. But then I mainly know academics.
Which brings me to another point. Within academia, the US is still considered the default centre of the world - but only just. But that has definitely changed in the last 20 years. 20 years ago, the status location for an international conference was the states. That is no longer the case. Many universities now prefer to hold conferences in the EU, and I've spoken to many scientists who now skip some minor conferences when they are held in the US, simply because they are in the US. This would, you assume, be bad for their careers, but two of them are leaders in their field. I'd say this is bad for the states.