On whether taxpayers have responsibility for the well-being of their neighbors, by means of government programs:
In the theocratic state envisioned by the Hebrew prophets (or even, in their critique of every nation) the responsibilities of kings was clear: plead the cause of the fatherless and widow, demand justice for the poor. See, for example, Psalm 82:3-4: Defend the cause of the weak and fatherless, maintain the rights of the poor and oppressed. Rescue the weak and needy; deliver them from the hand of the wicked. Nations were judged by how well their rulers implemented these simple principles.
In the United States of America, "we the people" (the voters and, yes, the taxpayers) are sovereign. Therefore "we, the people" are under divine judgment if we fail to use our sovereign power to take care of the elderly, the disabled, the orphan and widows of our world. "We, the people" as sovereign refers to our corporate role as king, which is to say, the government. It is laudable for individual persons to do what they can by means of "charity," but "we, the people" are not just an aggregate of individual persons. We, together, are king, and as such are answerable to God for how well we rule.
Been meaning to say this for quite a while, but I think it is well worth bearing in mind this August as "we" (in the royal sense) debate with ourselves about health care.