It should be kept in mind that the vast majority of the income tax revenue that sustains the US government comes from the "mass affluent", people who make a lot

It should be kept in mind that the vast majority of the income tax revenue that sustains the US government comes from the "mass affluent", people who make a lot of money (a few hundred thousand $ per year) but do get it from employment. This is the center of gravity of the tax system, the people who are in aggregate both well off enough and numerous enough to act as cash cows. Plus being employed limits tax shelters. So keeping the upper middle class taxpayers compliant should be the top priority of a competent IRS, irrespective of fairness. I don't know how focused on that they really are, but I would give them the benefit of the doubt without definitive evidence.