Libertas est Veritas:
Junker:What is the difficulty caused by massive income disparity?
Depends on the distribution.
Okay, there seems to be a fundamental misconception here. Income is not "distributed", i.e. it is not some fixed amount which gets spread unevenly throughout the population. Income is generated or produced, a consequence of one's acts of making economic exchanges. By specializing in producing one particular good or service in abundance, marginal utility kicks in for producers, and they are able to make beneficial trades of their product for everything else (or more specifically, money, which can then be traded for anything else). These trades are win-win, because each partner is trading something he values little for something he holds dear. Thus, income is created by the mutual beneficial exchange of goods/services produced under the division of labor (which allows marginal utility to lower the value of the product to the producer, allowing for beneficial trades). Even better, any income left over after consumption becomes savings, which becomes capital, which allows even more productivity and an even better standard of living. The rising tide lifts all boats (though the analogy breaks down when you realize that the faster, stronger boats somehow rise higher).
Now keep in mind that this is true only in an unhampered market. As you mention, we have a government out there picking winners and losers. The bulk of the losers happen to be the poor and middle-class (or as I prefer to call them, the "working" class), who are heavily victimized by the state, primarily by three methods, 1) overtaxation, 2) frivolous imprisonment and/or property seizures, and 3) currency debasement (this is not to say the state doesn't commit thousands of other offenses). This often results in a poor quality of life that is correlated with being poor or working-class, but has little to do with income per se. Most folks are making plenty of money to live good lives, if only the government would stop taking half of it and debasing what's left.
"He that struggles with us strengthens our nerves, and sharpens our skill. Our antagonist is our helper." Edmund Burke