New York Times op-ed, It’s Time to Rethink the Charity Deduction, by Richard H. Thaler (University of Chicago, Booth School of Business):

Now that Congress has actually managed to enact tax legislation, it may be time to consider some bigger issues. I hope that broad-based tax reform will be high on the list of both major parties.

Any meaningful reform will face intense lobbying from those who stand to lose. The tax deduction for charitable giving is a case in point. Although changes will be fought both by the givers and the receivers of tax-deductible donations, there is good reason to disregard their pleas. … I suggest three principles to help guide the debate:

1. The tax subsidy rate should be the same for everyone. This means that rather than being a deduction from income, the subsidy should take the form of a tax credit, so that if you contribute $1,000 and the subsidy rate is 15%, your taxes would be reduced by $150. (Ideally this credit should be “refundable,” so it is payable even if your tax bill is zero or negative.)
2. In the interest of tax simplification, the tax credit should apply only to donations above a certain minimum. The minimum could be, say, 2% of AGI. That way, only large contributors need to bother keeping records.
3. The tax credit rate should be kept low enough to prevent large distortions. If political considerations require that we maintain this subsidy, it might make sense to peg it to the capital gains tax rate, which is now 15%.

 N. Gregory Mankiw (Harvard University, Department of Economics) disagrees:

I think there is a bit more logic to current policy than Thaler does. Suppose you believe, as I do, that consumption is a better tax base than is income. Then, starting with a measurement of income, it makes sense to allow deductions for “non-consumed income”–specifically, saving such as IRA and 401k contributions and charitable giving.