I think the fellowships are a great idea: give money to people who have done excellent work. I am not sure of the motivations of the MacArthur Foundation, but if it were me I would trust by providing funds to those people they would (as a group, not every single person) take advantage of those funds to create great advances for all of humanity.
As I have mentioned before I also like, Trickle Up. While different in actual, to me there is a similarity: money is given that provides opportunity that I trust will make for a better world. The fellowship site does mention: “unrestricted fellowships to individuals across all ages and fields who show exceptional merit and promise of continued creative work” which indicates they do expect conduit creative work even though the fellowship is unrestricted.
It is great to see examples of those doing work worthy of such high praise.