Gerson's question

In his anti-Thompson op-ed, to which Michael linked here, Michael Gerson asked:

Should we increase the amount of money devoted to our generous cancer research efforts at the expense of African lives that can be saved for about $90 a year?

An interesting question, I think.

Now, I agree with Gerson that the United States should, for strategic and moral reasons, generously fund (effective, efficient, not-corrupt) development and health-care initiatives in Africa.  And, although I support Thompson's candidacy, I'm happy to agree that it was a mistake to answer the (inappropriate?) "as a Christian, as a conservative" question about President Bush's the global AIDS initiative (for which, it seems to me, he gets little credit) the way he did (i.e., by appearing to invoke Jesus as the authority for a particular application of Thompson's limited-government philosophy). 

Still, what about Gerson's question?  How do and should we allocate scarce resources among competing, worthy goals?  (It is not an answer, in my view, to say, "increase government's role and revenues" because, even if we do that, resources will still be scarce).  Can we justify, say, our space program, or the National Gallery, or expensive carbon-output-reducing regulations, given that, for relatively little money, we could provide clean drinking water to tens of millions of children, saving them from death and disease?  What criteria should we use? 

And, given that we do have to have some criteria, is it as obvious as Gerson seems to think that among the criteria a Christian may employ is not a (rebuttable) presumption in favor of responding first to domestic challenges?  Maybe so.  (Again, I strongly support -- for both policy and moral reasons -- generous-but-careful support for poverty-relief and development efforts in poor countries.)  But, if Gerson's right, then I suppose all those who support, say, labor and trade policies that put the needs of American industrial workers above the needs of workers in the developing world can expect a in-print spanking from Gerson, and a failing grade on his Christianity-test, too?