Years ago I argued here that since it could be proved that there is a duty to look after your fellow man in some limited senses, taxation to support a modest welfare net was justified. I was wrong. I didn't see the wisdom of the old maxim: hard cases make bad law.
I used corner cases in which it would be morally permissible for one person to force another person to help a third person who was in distress. You can imagine such a case. The one I gave went something like this. You see through a telescope that 100 yards away a small child is bleeding to death due to some accident. You cannot get to the child in time to save him because you can't move for whatever reason. A bystander is near the child but refuses to help him. You and the child plead with him, but he only shrugs. You have a sniper rifle and you are a marksman. You yell to the bystander, "Stop that child's bleeding or I will kill you." At this, the bystander complies. You've done nothing wrong.
This is a corner case. It is fun to think about, and it may even tell us something interesting about the moral duty of charity. What it does not do is anything at all to show that a government welfare net is justified. This is because it does nothing to overcome the prima facie case against concentrating enormous amounts of power in a few hands by law. In order to do that, you have to do more than put forward an odd corner case. For example, you might show that the power is necessary in order to save the very harmed by the concentration of power, as for, instance the founding fathers did when they argued for a powerful Commander in Chief of the U.S. military. But there is no such argument in the case of the welfare net. Moreover, a corner case does nothing to show that governmental power to enforce charitable duties would not, due to corruption and bureaucratic inertia, cause terrible injustices as side effects, injustices far outweighing the concerns of charitable welfare relief.
So, I was wrong and libertarians were right. I know of no good case for a federal governmental welfare net, given the urgent need to limit the power of the federal government and the capacity of private charity to address humanitarian needs.