I agree that national defense is valid expense for the Federal Government, but the US seems to take it too far. Why can every other country in the world manage to spend less on their defense than the US? The US spends many times more than other countries, sometimes an order of magnitude more. The military-industrial complex has grown much too large and has become a large drain on our resources.
Yes, the figure for war spending I quoted is over several decades, but we have already spent at least 1.5 trillion on the wars, all of it deficit spending. I am unable to find a corraborating source for your 2.6 trillion figure, the only other article I found referenced the Senate Budget Committee (republican members) http://www.budget.senate.gov/republican but I could find no reference to this material on their site. I would be more inclined to believe the CBO than a partisan committee, and the CBO says its projections have not changed very much in the years since the passage of the legislation (http://www.cbo.gov/publication/43104). Notice the net budgetary impact graph at the bottom of the page, It is projecting the effect of the legislation is a reduction of the deficit in contrast to the war spending which only added to the deficit. Not only are we paying for the wars now, we will be paying for them far into the future. At least when we pay for health care each year we get something back for our money, any benefits from the wars will be long gone by the time we pay for them.
National defense is a necessary part of a nation-state, but how did attacking a country that had nothing to do with 9/11 and didn't pose an immediate threat (false claims of WMD notwithstanding) promote the security of the US? A major impetus behind the 9/11 attacks was the previous foray into Iraq and our backing of the House of Saud, our current foray into Iraq will no doubt have similar consequences in the future. You're welcome kids!
In the world in which we live, giving up defense to provide healthcare is likely to mean eventually you are likely to have neither unless you have a strong benefactor to protect you. The US has played the role of benefactor to Europe since the end of WW2. Who will protect America if it gives up its own defense?
Nobody is saying the US should give up its defense, but maybe it should just defend itself rather than providing defense for foreign countries. Also, calling pre-emptive attacks "defense" is massively stretching the meaning of the word.