Some recent polls have suggested most Americans believe the 1st decade of the 21st century to be the worst decade in the past 50 years. The polls appear to ask people the source of this belief, and most people point to 9/11. However, I think that there is a more pernicious and creeping source behind this pessimism. Americans now are less responsible for the content and direction of their lives than in the history of the country.
Think about how much of American life is regulated and directed by government at all levels, from cradle to grave. The hospital in which you are born may be a state hospital, but even if private the funding for the hospital is affected by government regulations (e.g. it is organized as a non-profit for tax purposes; you pay for your procedure through a combination of self-pay and employer-based insurance).
Growing up, your education is either through a public school or a private school that the state has allowed to exist (e.g. charter school). No matter the choice, your parents and/or the community around you pay property taxes to finance schools. You can even start going for day care and "early childhood education" quite early on in life, again government/tax financed. If private ones exist, they must generally be licensed by the state.
Once you enter the work world, income is taxed, goods you purchase are taxes (remember, you pay the corporate income tax through the price of goods and services consumed), and there are a variety of payroll taxes. These payroll taxes go to things like social security and unemployment insurance - two social welfare constructs that further reduce peoples' responsibility for the future. Part of taxes are also directed to equalization payments, like tax credits or welfare, which also reduce peoples' responsibility for their own choices.
There is an argument for a social safety net, and there is a duty to protect the weakest members of society. But all of this removal of personal responsibility for those who are capable of running their own lives is long-run damaging. It is, I believe, the source of American pessimism. We've gotten to the point where we expect another entity, usually a government or one of its agents, to solve our problems. This removes the feeling of accomplishment and success, so crucial to happiness.
Another problem with such high government involvement is the crowding out of communities that used to exist to help people who got 'in a bad way.' Fraternals, mutuals, etc. have shrunk to be almost nothing, a distant memory for some, an unknown for most. I hesitate to say "secularization" here, because many of the communities were not religious in nature. But a sense of belonging to the larger community has diminished a great deal and I think this also has a lot to do with a sense of disconnection and general malaise.