Ya know, over in the Scandinavian countries like Denmark, they don't have 47%-ers.  Their 50% tax rate hits income over about $3,000/yr, and the top rate peaks out at about 60%.  Everyone pays into the system at pretty much the same rate.  Almost a flat tax.  The result: among the highest rates of credit card debt, consumption of anti-depressants, and alcoholism in the world.  The suicide rate has dropped from one the highest to close to our rate after the government started handing out anti-depressants like breath mints.

The biggest "loophole" we have in our tax system that costs the government the most revenue is the standard deduction and personal exemptions.  That's why we have a 47%.

The next two biggest, most costly loopholes are (a) tax free treatment of the employer-paid portion of group health insurance premiums, and (b) the mortgage interest deduction.

Still want to eliminate loopholes?  The people who benefit the most from loopholes are middle and lower class.