His older brothers are jealous of Joseph because of Jacob's favoritism, and perhaps angry at Joseph because he is an arrogant, insensitive, tattle-tale (Gen 37: 2). But that is not sufficient to explain their willingness to murder him. The main cause of their enmity is probably inheritance and dynastic rivalry. By giving Joseph the coat-of-many-colors (and giving nothing comparable to his other 11 sons), Jacob signals his intention to make Joseph his heir rather than dividing his estate among his children. Anticipating his inheritance, Joseph predicts that he will eventually rule over his brothers (Gen 37:5-10), and his older brothers plot to prevent this outcome.
Now Israel [Jacob] loved Joseph best of all his other sons, for he was the child of his old age; and he made him [a coat-of-many-colors]. When his brothers saw that their father loved him more than any of his brothers, they hated him so that they could not speak a friendly word to him. (Gen 37:3-4)
Jacob's gift and estate plan are clearly bad for the brothers, the family and even for Joseph. The gift and plan incite negative feelings of hatred and resentment in the brothers, disharmony and eventually violence, between family members and self-importance and a sense of entitlement in Joseph. The brothers are bitter, the family is rent with faction and Joseph is a spoiled child.
But are Jacob's gifts and planned bequest to Joseph unjust?
In hindsight, Joseph's older brothers are hardly entitled to complain, but let us suppose that Jacob is unaware of their murderous tendencies. Jacob is partial to Joseph because Joseph is "the child of his old age," but the Bible does not suggest that Jacob considers the brothers to be flawed people, or Joseph to be a likely leader.
Common sense does not insist on an equal distribution of goods among one's children. One might give more to needier children, for example. Equal opportunity is a better goal than equal shares. Additionally, one might give more to children who are more helpful to the family. Those who contribute to the common good arguably deserve compensation. How to balance these (and other) considerations is unclear. Many ways of combining them would be reasonable. But this much is clear. Common sense says that there are unfair ways of giving and bequesting to one's children, and Jacob's way is unfair.
Libertarians disagree. They say that there is nothing unjust about Jacob's gift and plan, or almost any gift and plan, for that matter. It is Jacob's property, after all. So long as he doesn't use it to fund murder, assault, theft, or restrictions of liberty, he can do whatever he likes with it. Playing favorites is not unjust.
Joseph's coat-of-many-colors highlights the counter-intuitiveness of libertarianism. The common sense principle of compensating for need in order to equalize opportunity within a family, and the principle of rewarding contribution to the family clash with the libertarian principle that people are free to give and spend as they like. When siblings complain that a gift or will is unfair, common sense is open to the possibility that the complaint has merit, but libertarianism simply dismisses the complaint.
Generalizing principles of justice from the family to the nation?
Jacob's sons are not just twelve individuals; they stand for the twelve tribes. Indeed, the Bible's use of Jacob's other name, Israel, indicates when it is speaking both about individuals and about the Israelite nation. In particular, when the Bible censures Jacob's gift by showing its unfairness and harmfulness, the Bible is also treating the brothers as symbols for their tribes, warning the Israelites of the disastrous consequences and injustice of partiality at the national level.
The Bible is drawing the following parallel. Just as partiality within a family damages the disfavored, the favorite, and the family as a whole, so disparities (unjustified by need or contribution) within a nation damage the disadvantaged, pervert the character of the advantaged, and generate enmity and violence.
Partiality is not only harmful; it is also unfair. Just as it is wrong for parents to use gifts and bequests to play favorites within a family, so it is wrong for people to use gifts and bequests to play favorites within a nation. Well-off parents should equalize opportunity and reward the helpful among their children. Well-off people should equalize opportunity and reward the helpful among the nation's next generation.
Of course, the Bible is not completely prohibiting people from favoring their own children over the children of others. Such extreme impartiality would be too demanding, and the Bible does not demand the impossible (Deut 30:11-14). A reasonable interpretation is that we should temper our partiality, impose boundary constraints on giving and bequesting. We should combine the principle that people may give and leave their wealth to whomever they choose (often their own children), with the principles of compensating the needy and rewarding contribution. Do your share to equalize opportunity and reward the deserving; do what you like with the remainder of your wealth.
Of course, identifying the needy of a nation, determining how to equalize opportunity, recognizing the contributors, and measuring the worth of their contribution are tasks beyond most people. Moreover, at least some people will not do these things voluntarily. How can the uniformed, the unskilled and the unwilling be induced to do the right thing?
Enforcing justice is the role of government. Government should take steps to make giving and bequesting fair. Thus, the story of Joseph's coat-of-many-colors provides a rationale for a gift tax and an estate tax -- taxes generally opposed by Libertarians. With the proceeds of these taxes, government can fund a partial safety net for the needy to equalize opportunity (e.g. food stamps), and a set of benefits for the deserving (e.g. GI bill).
As Amy March says, "I don't think it's fair for some girls to have plenty of pretty things, and other girls nothing at all." (L. M. Alcott, Little Women).