Why we fight

Yesterday, the US Senate failed to pass a defense bill which included, among other things, the repeal of the Don't Ask Don't Tell (DADT) policy in the military. Before the bill was shut down, Arizona Senator John McCain said in criticism of Democrats who are in favor of repealing DADT:

"...to use a bill that has to do with defending our national security interest when we're in two wars to pursue a social agenda...is reprehensible."

There seems to be something wrong with that statement. The arguments that McCain's fellow hawks have offered in support of America's present and past wars include the spread of liberty and democracy, preserving the American-way-of-life and othersuch social values. If this rhetoric was to be believed, it follows that America fights wars for the promotion of social agendas. Why, then, is Mr McCain complaining?