A couple of reasons:<p>It&#x27;s better for society if the rich give money to medical research and the like rather than buying yachts and jets so why not encourage it.<p>If they taxed donations you could achieve the same effect tax wise by say Facebook spending money directly on medical research - $1bn blown on reseach is $1bn less taxable profit. But it&#x27;s messy that way. The present system&#x27;s cleaner.