Refutations of Peter Singer

[Linkman226]

I'm looking for refutations of Singer's view that charity is a moral obligation. I remember reading one by Nozick (at least I think it was Nozick) some months back but I can't seem to find it. I'd very much like original sources. I can access JSTOR so links from there are OK. Also, I was wondering what you guys thought about Singer's view. I'll quote him:

I begin with the assumption that suffering and death from lack of
food, shelter, and medical care are bad. I think most people will agree
about this, although one may reach the same view by different routes.
I shall not argue for this view. People can hold all sorts of eccentric
positions, and perhaps from some of them it would not follow that
death by starvation is in itself bad. It is difficult, perhaps impossible,
to refute such positions, and so for brevity I will henceforth take this
assumption as accepted. Those who disagree need read no further.
My next point is this: if it is in our power to prevent something bad
from happening, without thereby sacrificing anything of comparable
moral importance, we ought, morally, to do it. By "without sacrificing
anything of comparable moral importance" I mean without causing
anything else comparably bad to happen, or doing something that is
wrong in itself, or failing to promote some moral good, comparable in
significance to the bad thing that we can prevent.

This is for my school's debate team, if you're wondering.