Obama having it both ways with tax rates

I just got done watching (the rather dull) Obama news conference, and something caught my attention about Obama's position on the tax deduction for charitable giving:

And what we've said is: Let's go back to the rate that existed under Ronald Reagan. People are still going to be able to make charitable contributions. It just means, if you give $100 and you're in this tax bracket, at a certain point, instead of being able to write off 36 percent or 39 percent, you're writing off 28 percent.

...

And so this provision would affect about 1 percent of the American people. They would still get deductions. It's just that they wouldn't be able to write off 39 percent.

In that sense, what it would do is it would equalize -- when I give $100, I'd get the same amount of deduction as when some -- a bus driver who's making $50,000 a year, or $40,000 a year, gives that same $100. Right now, he gets 28 percent -- he gets to write off 28 percent. I get to write off 39 percent. I don't think that's fair.

So Obama seems to be arguing for tax deductions to be "flat"--for a person making $50,000 a year to receive the same percentage deduction on charitable giving as a person making $500,000. But this is just the converse of the flat tax! The same logic that argues for a progressive tax structure on the disincentive side also argues, conversely, for a regressive tax structure on the incentive side. In other words: if we can tax Bill Gates a higher rate because giving up 39% feels way less painful to him than it does to me, then we must also incentivize Bill Gates at a comesurately higher rate, because his gaining 28% feels way less pleasurable to him than it does to me.

(Related post here.)