Someone said it is selfish, unjust and unchristian that the Australian Government allocates so little money to foreign aid.
I think we need to be careful about the use of the word "unjust" these days.
If someone refuses to help others, by all means we might call it "selfishness" or "unchristian". We might even call it "ungracious" or "unmerciful". But calling it "unjust" might put us at risk of subtly implying that other nations somehow have a right to an Australian citizen's money.
That would be similar to if you had graciously chosen to give someone a Christmas gift, yet they happened to think you hadn't spent enough on them. They could call you "selfish" and "unchristian" if they want to - but they wouldn't have the right to call you "unjust" - because that would imply that your gift never truly belonged to you in the first place; it would also mean that your giving was never truly a "gift", but was merely an administrative redistribution of public property; and it would imply that you had actually become a thief, because you had witheld for yourself something which someone else actually had rights to.
If someone witholds some of his own personal property from a needy person, the Bible might call that person "ungracious" or "unmerciful". It's only if a person retains someone else's own rightful personal property that the Bible would call him "unjust".
Any morality of redistributionism which subtly confuses "ungraciousness" for "injustice" becomes the seedbed of various levels of socialism and communism.
By all means let's go all-out for selflessness and generosity. But what is unjust, is a morality which teaches that someone else has rights to your personal property. And it's a mentality that perpetuates rather than alleviates poverty.