Actually it may work. The only ones deterred by this notice would be those who donate to feel entitled, but not those who do it to show genuine appreciation for his work. And I doubt former kind even makes it to the donation form in the first place.

A feeling of entitlement does not work that way. People aren't that rational; they don't donate for the purpose of having a say in what happens. They probably donate for honorable reasons, but once something they want becomes an issue, they feel entitled because they donated.