Part of the reason people believe things like the views of Mickey Kaus that I described in my last post is that they have strong intuitions on the matter. It seems initially plausible to many that we have a greater duty to help our co-citizens improve their lives than to help those of other nations. I have never shared such intuitions, for whatever reason, which is one of the reasons I speak strongly against them; I don't find them to have even prima facie plausibility. I recognize that many people do find them plausible, though, so I do consider them worth discussing.
I do have other intuitions, which shape the moral principles I accept. I think there are many persuasive thought experiments, for example, which count persuasively against consequentialist moral theories. But just because we have an initial negative reaction to a specific theory is not significant enough reason to discount it. Moral reasoning does not stop at the intuition.
For example, many consequentialists have error theories to attempt to explain away why I find the implications of consequentialism to be counter-intuitive. And some error theories are bound to be correct, because sometimes we have opposing intuitions about the same principle, and they cannot both be accurate. But the error theory has to be more plausible than the intuition itself; whether or not this is the case will be the subject of much disagreement, of course, but these are things about which we can have fruitful discussion.
Many people have the intuition that it is not wrong to kill non-human animals. I think they are greatly mistaken, and have argued as much many times. One of the most convincing arguments for this position, in my opinion, is that argument about speciesism. If I am right that speciesism is analogous to racism or sexism, in that it makes moral distinctions based upon irrelevant criteria, then we ought to be strongly suspicious of our initial intuitions about our obligations to animals. If we can then find a plausible theory that explains why animal death is bad, with the strongest objection being an appeal to initial intuition, then we ought to accept the badness of animal death (and hence the wrongness of killing them.)
Similarly, we should be very suspicious of views, like those that Kaus holds, which privilege one group in a certain way. We know this is one mistake in moral reasoning that people frequently make. And one of the common signs of the deficiency of such views is the weak arguments that Kaus gave to support it; basically, he appealed to his intuitive reaction, and then said his view would be "easier" to achieve anyway. Hardly a compelling case.
Increasing legal immigration to the United States would be extremely beneficial to the world. Immigrants here often live better lives and make more money (that's why they want to come), and then they send some of that money to help their families back in their home countries. They bring demand for goods and services here, provide labor, and help increase the wealth of their home countries. If we're worried about the demographic trends of an increasing elderly population, immigration can help solve this problem too.
You might worry that a large influx of immigrant might significantly change our culture, and there might be legitimate reasons to want to preserve culture. But it seems obvious to me that the benefits far outweigh the potential losses.