The original question posed is really the same as asking, "Is there a biblical mandate for government-sponsored welfare?" And I just don't see it.
The "render unto Caesar" scripture can be used only to justify paying taxes as opposed to avoiding taxes. So Christians should pay any taxes levied.
Someone mentioned Jesus's feeding of the 5000 early on in this thread as an example of Christ initiating a welfare program. He really wasn't, though. He was performing a miracle: according to Matthew, Jesus fed 5000 men (not counting the women and children also fed) using only two loaves of bread and five fish. This miracle was akin to the poor woman whose one bottle of oil miraculously filled every liquid container in the house.
If we look at the Old Testament welfare system from the book of Ruth, we see a system that does not simply give assistance to the needy. The Israelites were to leave the corners of their fields unharvested. Ruth meets Boaz because she is harvesting the corners of his fields to feed her mother-in-law and herself.
My two biggest complaints concerning our welfare system are the incentives it produces and the lack of constitutional mandate.
As has been stated before, welfare creates no incentive for recipients to reclaim their independence. It creates (or used to, if they've changed the law) incentive for families to have more children, as the payments go up with each child born. Finally, it creates incentive for those who are barely surviving financially on their own to quit work and go on welfare. As Cinci implied on page 9 of this thread, knowing how much these incentives should matter is easier said than done. I think the incentives I've discussed really boil down to welfare's interaction with basic human nature.
The fact that the Constitution enumerates certain powers to the federal government and reserves all others to the states should make us wary of the constitutionality of federal assistance. If states want to have welfare programs, fine. They'd probably be better able to react to the needs of their citizens. But the federal government should not. Now, Sepia will probably be able to give a very good rundown of why welfare is constitutional (please, Sep, say more than "it's in the preamble"). I'm looking forward to reading it.
In short, 513, I am a Christian who is opposed to a federal welfare program based on economic, philosophical, and constitutional objections. I reject your premise that I oppose welfare in spite of my Christianity. Rather, I oppose welfare (in part) because of my Christianity.