I am sure that many calculate the deduction when calculating how much to give.
Probably true. But wouldn't we be in a much better world if everything would be considered just on its merits, rather than ulterior benefits? The tax code, which is bloated and convoluted, is a hindrance on American Exceptionalism, and so many other values which are the basis of the establishment of the US form of government.
Don't get me wrong. I directly benefit from this convoluted situation. People consult with me, and taxes are very often a major part of the equation. But the fact that so many accountants, lawyers, and other professionals benefit from it, not to mention the huge Washington bureaucracy that lives off it (even if we talk only about the IRS), doesn't make it right. There would be paid if we moved to a flat tax, or a consumption-based tax TO REPLACE the entire current IRC, but that paid would be soon forgotten by the growth and opportunities created.