Would a person stop donating $1000 of their expendable wealth to their favorite cause (e.g., hunger, cancer, cloning hitler, whatever) if that $1000 donation no longer reduced their taxes by $200 (for example)? If so, what kind of person would do that? Probably not the kind of person who ever donates to anything in the first place.

Worst case, if there were no more tax-deductible charities: that person would pay the $200 taxes and only donate $800 (instead of $1000) to their favorite cause. Best case: Megawealthy would no longer leave $20 billion to their favorite cause (be that their dog, the LDS church, their love of oil drilling, or whatever), but would pay $5 in estate taxes and only have $15 billion leftover for their love of oil drilling (or whatever be their whim).