I agree, it definitely is sustainable for certain types of content. However, even NPR has donation campaigns where they are running ads for themselves and they also run ads for other companies that support them. I guess if they were forced they could change this habit.

> Sam Harris' podcast runs entirely on donations

He seems to be shifting away from that. There is a "private feed" that will "increasingly carry content that will not be available on the public one" (from first 20sec of Making Sense #168). So yeah, he either wants more income or just donations isn't that great.