In that case, the issue might be in functionality and purely political/legal in nature. Education is suppose to be a state and local matter, for example (schools get money from property taxes.) It is in the constitution that education should be a state power. This is for obvious reasons (so propaganda can't be imposed in schools by a federal power.) Additionally, many people viewed the federal government's involvement with "No Child Left Behind" as a waste of tax dollars, because other countries found better results with less money. Hence, one might argue for the federal government to provide vouchers to enable the choice of private schools instead of giving additional funding to public education. In 2007, in example, because of the dependency on the federal government for "No Child Left Behind" funds, many states were left to dry when $75 billion was moved elsewhere in the budget. Furthermore, such funding gives the federal government more say in the control of certain states than others (those which receive money.)
I think most Americans oppose social democracy because they view it as a means of dependency on government, which many do not like at all because it creates a strong federal state and one which will have more control over people's lives. Americans are far more individualistic than Europeans, and I assume other ex-British colonials. In general, the Classical Liberal sentiment is still strong, albeit not in politics. There is also a strong federalism ideal in place, in which state rights shouldn't be infringed upon by federal rights. The label of "socialism" is just a media tool by the right in general to make social democracy scarier.
As for healthcare, the issue with Obamacare is mostly the mandatory purchase. The majority of Americans oppose it because it is unconstitutional and the government shouldn't have power to force people to purchase health care (or anything for that matter.) Furthermore, it hurts the private health professionals (only covers some of the cost) so they refuse to take it, hence making it useless. This is why you see many state governments nullifying it, or attempting to. The biggest problem is the fine ( or what they call a"tax".) Discard that, and I think most people would be happy with it, as they are happy with the current Medicaid/Medicare already in place.
And then I think all, except the neo-conservatives and their followers, agree that our military spending needs to decrease and we need to bring most of our troops in the world back. For far too long Americans have been paying for military bases in countries that are at peace and can put their own money into their own military.
Those are the three largest investments by the U.S Federal government. After they're adjusted, I think it is quite clear that spending would be reduced regardless of whether it is necessary or not, and debt can be paid off. However; the way things are going right now can't persist.
