The case for equality of wealth – or rather, the case against excessive inequality of wealth, since absolute equality is not the goal – is not a case of fairness, but rather, a case of compatibility of parties entering the social contract – i.e. forming the state. There is no need for a lion to enter a contract with a pack of mice, and so, when a single party manages to amass monumental wealth, they lose the necessity of entering the social contract with the populace below them. The façade of the contract is maintained, but the power afforded by wealth cannot be contained, being used to exert influence over public affairs. Power afforded through wealth destroys political boundaries established by the mutual contract between the citizens of a state, and thus, through corrupted individuals – those accepting the bribe being all the more guiltier for betraying their role – inequality of wealth leads to inequality of rights.
The problem is dire, for either of the two obvious solutions lead to their own undesired ends. Remove power by curbing wealth and you do a great injustice to those who have earned it by honest means, as well as those who did not abuse their position. Leave excessive wealth as it is and you leave the state vulnerable to bought power, doing injustice to honest citizens who are forced to serve the will of a state that doesn’t represent their interests. Additionally, the act of curbing wealth itself is prone to myriad problems, as is any endeavor in which great amounts of unearned money change hands. You seek to disarm the lion but end up feeding a pack of wolves.