I understand what you are saying. However, when people give or ask for donations in response to an international disaster, for instance, the government already has a policy of matching individual contributions. So it is a type of tax credit, but in the form of a direct subsidy related to the donation.
I am trying to see how a donation in response to an international disaster can be considered the same as a donation made to a charitable organization as presently conceived. I could make the case, for instance, that a donation to a political party or a tax credit for the arts, for children or for sports, both fall into a different category that is not the same as donating to a charity.