Why the obsession with Mitt Romney’s tax returns? It’s not because curious voters are worried they have a “flawed candidate,” as Rick Perry suggested last night. (a) We already know we do (no matter who we choose!) and (b) Mitt Romney is not a tax evader. No, curious voters want to know two things: (1) Just how high is Romney’s annual income? and (2) Does Romney pay more or less in taxes than they do?

Romney hinted at the answer to the second question this morning at a press conference in Florence, S.C.

Romney said he “probably” pays only about 15 percent in federal taxes because most of his earnings come from capital gains, which is taxed at a lower rate than traditional income. This means the super wealthy Romney pays a significantly lower tax rate than most middle income Americans.

ThinkProgress, the blog of the liberal Center for American Progress, goes into more detail:

As Center for American Progress Director of Fiscal Reform Seth Hanlon has explained, the latest data shows that “many middle-class families paid much more [in taxes] than the 17.5 percent average paid by the very rich.” When President Obama suggested the “Buffett rule,” aimed at ensuring that millionaires can’t pay lower taxes than middle class families, Romney derided it as “class warfare,” and “the wrong way to go.”

One of the reasons Romney is able to drive his tax rate down so low is that he is still earning money from his private equity firm, Bain Capital, that is likely subject to a pernicious tax loophole. This loophole lets wealthy money mangers like Romney pay the capital gains tax rate on profits they make investing other people’s money, turning the justification for having a lower capital gains tax rate completely on its head.

Such loopholes in the tax code aren’t Romney’s creation, however, and, honestly, it’s highly rational of him — and of any member of the ultra-rich — to obey the incentives created by the tax code. No one argues the tax code is not in need of reform. The question becomes: Do we close loopholes to raise rates or do we close loopholes to lower rates? By all means, let’s make the tax code fairer — but let’s do it in a way that still encourages earning and investment.

Meantime, Romney’s tax returns matter far less than his policy proposals. May Romney’s “I probably pay 15 percent” quip please suffice to satisfy curiosity about his personal taxes so we can return to the real issues — even if one of those issues is itself tax reform?