Cain said to his brother Abel, "Let us go out in the field." When they were in the field, Cain attacked his brother Abel and killed him. Then the LORD asked Cain, "Where is your brother Abel?" He answered, "I do not know. Am I my brother's keeper?"
-- Genesis 4:8-9
The next time you find yourself in debate over social issues with a religious Christian conservative, remember the story of Cain and Abel. God doesn't directly answer Cain's question, but in fact the remainder of the five books of Moses can be seen as an answer to Cain in the affirmative.
Maimonides (Rambam) wrote in Mishneh Torah, Laws of Gifts to the Poor, 8:10, back in the 12th century:
The redemption of captives takes priority over sustaining the poor and clothing them. Indeed, there is no greater mitzvah than redeeming captives, since captives fall under the category of those who are hungry, thirsty, and naked, and their lives are in danger. Anyone who ignores the plight of captives transgresses [many negative commandments, including]: "do not harden your heart and shut your hand against your needy kinsman" (Deuterenomy 15:7); "do not stand idly by the blood of your brother" (Leviticus19:16); "do not rule ruthlessly over [your kinsman]" (Leviticus 25:53). In addition, he fails to fulfill the positive commandments, "open your hand to the poor and needy" (Deuteronomy. 15:11); "your brother shall live with you" (Leviticus 25:36); "Love your neighbor as yourself" (Leviticus 19:18); "rescuing those taken off to death, those condemned to slaughter" (Proverbs 24:11), and many others. Indeed, there is no greater mitzvah than redeeming captives.
There can be no disputing God's answer: We are each of us our brother's keeper. Several thousand years of biblical tradition back up that analysis; anyone who would dispute this must prove their case.
Conservatives typically answer this by claiming that voluntary charity can take up the task. The problem with charitable giving is that it is never adequate to the task of providing for everyone who needs it. Charitable giving never meets the monetary needs of the programs. Further, charitable giving dries up when it is needed most--in years of economic difficulty. Finally, voluntary charitable organizations simply cannot cover everywhere, all the time.
Should access to charity be a lottery of geography? I think not. Only government can provide the coverage, the funding, and the equity of access that really make a difference in my brother's lives.