If one cares about that goal — “reduce the size of government to the greatest extent possible” — then supporting the limitation of deductions today without some broader reform won’t do it. After all, what is the purpose of the folks in the administration proposing this change at this moment — is it to limit government? The Obama administration proposes removing these deductions to fund a large expansion in government. They’ve been pretty explicit about it. So at best it’s a wash, and in the case of philanthropy it will actually expand government at the expense of civil society — a net negative.