In that case we didn't screw up, we just didn't enact policies necessary to cause a middle class to flourish or keep it relatively easy for new people to enter the national economy with ease as we once did. Our system has always been designed to make the rich richer and the sufficiently poor poorer, it is just that we've gotten to a point where enough wealth is distributed among a few enough individuals so that they can control too significantly peoples ability to achieve the american dream or allow the poor and middle class to climb the ladder.
If a few enough people control enough of the wealth they can influence how easy it is for the rest of the pariticipants in the economy to achieve the american dream, and since there are only so many luxuries to go around there is actually not enough of them to give to the people under them per such-and-such period of time. Also, if enough of the money is controlled by few enough people they can simply control how much wealth gets distributed to classes lower than them.
This was not an evil design or anything, it is just that for the last several hundred years, that is how our economy works. It worked before because the wealth was more evenly distrobuted and we had fewer people, and it has worked for us up to and including now, but it is becoming more and more obvious that the rich have too much power and there isnt enough to go around for the rest.
Basically a few select lines of people started first, they've been accumulating wealth and they are now in control. This was caused simply by them starting first. Our economy didn't screw up, it was designed in an unsustainable way in the first place.
