"ie are there reasons to not act in a selfish manner 100% of the time."
Certainly, but the feeling I get from the original comment is: "There are no reasons to act selfishly ever." I'm not arguing in favor of 100% selfishness; I'm arguing against a zero-tolerance policy towards it.
Further, the form of the whole thing is troubling. If someone asked you, "How should we help the impoverished citizens of X?" My first response would likely be foreign aid of some sort, or perhaps free trade. But I don't get the feeling that proponents of open borders would be satisfied with those (assuming for the sake of argument that they would indeed help). Beggars can't be choosers; the focus on one method makes it feel more like a shakedown than a plea for help.