Inequalities in income weaken social adhesion

Why should it matter if there is large gap between the rich and the poor? This article points to two reasons:
-increasing inequalities decrease social adhesion
-increasing disparity in wealth is historically indicative of a looming depression

The article points out that America is heading toward 'developing nation' levels of inequality.

Why and how is this happening? The book "The Trap: Selling Out to Stay Afloat in Winner-Take-All America" by Daniel Brook posits that a movement in in the '50s is responsible. An exerpt from a book review explains:

Today's inegalitarian America was intentionally built--or more accurately,another America was intentionally destroyed. In the decades after World WarII, America became a middle-class society of broadly shared prosperity.Teachers and factory workers and lawyers often lived in the sameneighborhoods as progressive taxation pushed incomes closer together...Widespread unionization ensured that a rising tide lifted most boats. Jobswith pensions and health care were common and attainable. Eventually,long-overdue efforts to make American institutions meritocratic and open towomen and minorities began to build a truly egalitarian nation.This prospect fueled a conservative backlash. Despite his slight tendency tocaricature the motives of mid-century conservatives, Brook does compellinglyreview the movement started by William F. Buckley's 1955 founding ofNational Review, a publication with the stated goal of standing "athwarthistory, yelling 'Stop!'" Five years later Young Americans for Freedom, agroup that promoted laissez-faire capitalism and "militant anticommunism,"held its first meeting <http://www.yaf.com/history.php> at his Connecticutestate. Formed at a time when "conservative" was a dirty word in Americanpolitics, YAF chafed at the widely-held view, inspired by FranklinRoosevelt, that governmental power should "be used to level the playingfield, to make the promise of freedom real for all Americans." YAF's view offreedom was different; freedom was simply "the power to spend your moneyfree from interference from the government."Buckley and his ilk quickly realized that this sort of language could beadapted to the middle class, despite the fact that it was the rich who weremost affected by the tax code of the 1950s and 1960s. This was a monumentalmoment for the conservative movement. Even today, conservatives remainsuccessful at exploiting the specter of excessive taxation againstmiddle-class people whose most pressing economic concerns--the spiralingcosts of education, health care, and housing--are in fact exacerbated by taxcuts at the top. Taxes, in short, are rarely the reason a middle-classfamily struggles. But conservatives were able to craft a new rhetoricalconception of "freedom"--a conception in which the issue of taxation trumpedall concerns of building a fairer society.

Are tax-cuts for the rich the cause of the problem? Is it apathy or lack of guidance and support in lower income areas? What do you think?