One thing that's worth some consideration in discussions of 'distribution of wealth' is the function of wealth in a capitalist economy. We tend to be preoccupied with the creature comforts wealth can buy us, but under capitalism, the real power of wealth is control over labor and resources.
The key question that any economic system must address is "what do we do?". What should we work on? What products should we produce? That sounds obvious, but the way this works in capitalism is actually quite subtle.
To see the issues involved, it's helpful to look at the question first from the perspective of a non-capitalistic economy. Under a state run socialist economy these decisions are made by government. Whether or not the things you want (the blue jeans you like, your favorite TV series, the medicine you need, etc ...) get produced in sufficient quantities, is fundamentally a political question. It depends on the will of the majority and the decisions of our elected leaders.
Under capitalism, this power is 'privatized'. Each of us has the ability to influence these decisions approximately equal to the amount of wealth we control. At the most personal level, we express this power through our consumer choices and our career decisions. We 'vote' for what we value by deciding how to spend our money. We choose what we do for a living, in part, based on the desires of other people with money to spend. At a broader level, those who can 'concentrate wealth' gain more power to influence our economic direction. To the extent that they can persuade others to give them money (by providing them with something they want), they gain more economic power. If they fail to do things with their money that other people value, they lose it. Capitalistic decision making is, ultimately, a communal process.
So, what's going on with the 'concentration' of wealth? Assuming that private property laws are soundly supported, and assuming the freedom of each individual to spend their money according to their values is protected, people who manage to accumulate wealth do so by spending it (i.e. directing the production of goods and services) in ways that society values. We express our approval of their decisions by the way we spend our money.
Whether we see concentration of wealth as good or bad depends on whether we think the people controlling that wealth are making good decisions or not.
Now, obviously the above is the ideal, and depends on a government that protects private property and our freedom to spend our money in accordance with our values. When either of those are compromised, whether through outright crime or misguided laws, the balance is disrupted.