Socialism. Because that is what income equality basically is. It leads to massive unproductivity.
And your rational is erroneous, outdated econ 101 gone rogue: Income inequality in itself is nothing bad. And it is natural and desirable. Because we are all born with different skills, different passions, and we are all born with a free will. We can choose to work hard and attain something in life or we can choose to be complacent and reject continuous education, retraining, ...it is a free choice. Which leads me to argue that not everyone should be compensated equally for their labor because different efforts went into such labor. Hence paying and compensating people differently is desirable, else nobody would want to attain the harder to attain qualifications, needed, to perform a certain job. Why would you undergo med school and work your butt off for years without pay to get your med qualifications if you are promised the same low pay of a grave yard digger? You would never bother with med school. I think this whole argument completely disproved your points.
I continue to claim that it is the lack of opportunities that really strangulates an economy. The truth is that not everyone with equal qualifications will get the same opportunities. Put two applicants into one room, one Jew, one Black guy. I promise you that in virtually all cases the Jew will be taken for an investment banking job at Wall Street. For no apparent qualification related reason, but nepotism. Put a woman into the same room with a male sports athlete and let them compete for a trading position. Again, otherwise identical qualifications. Yet, it is very apparent that in most cases the guy is taken.
Lack of opportunities are not always character or race/religion related. Often times it is because the lack of opportunities creates a chain reaction. Some parents simply cannot afford the education of a private boarding school which unarguably offers a better education than a public school in a slum neighborhood. So, this lack of equal opportunity almost certainly places an applicant for a Wall Street job, for example, on the bottom of the list of applicants, with all the other candidates having attended pristine private education. Not that this would be a hindering point to a strongly driven person to succeed but it simply presents unequal opportunities.
@sle perfectly described it, privileged upbringing does not force someone to work like nutcase in order to attain certain opportunities, but someone on the bottom rung hardly ever is presented with such opportunities to start with and most often it either requires an incredible amount of luck or an iron willpower and effort to otherwise shine, or both.