I'm almost positive that Romney isn't releasing his tax returns because they'll show he paid a ridiculously low effective tax rate for many, many years.
In 2010, the only year he's released, Romney paid an effective tax rate of 13.9 percent. That's basically the same as the marginal tax rate paid by a married couple earning $17,400 – $70,700 (give or take). The Romneys earned $21.6 million in 2010.
Some experts are speculating that Romney's other returns could show an even lower effective rate.
And then he's going to tell his followers that taxes in America are too high? Hilarious.