I wouldn’t state the motivation for a “diverse charity portfolio” as positively desiring warm fuzzies—rather, I think the aversion to a mixed set (note that I doubt we would usually want an only-hands-on set of charities—too much work and would feel like pushing a boulder up a hill) is about potential exhaustion at repeatedly doing the one “most efficient” thing to the point that you’re not taking 60 seconds of mental refreshment. Psychological viability is the missing element here, causing us to intuitively sense that the proposal isn’t actually best, utility calculation be as it may (the actual calc would not have such problems).
I wouldn’t state the motivation for a “diverse charity portfolio” as positively desiring warm fuzzies—rather, I think the aversion to a mixed set (note that I doubt we would usually want an only-hands-on set of charities—too much work and would feel like pushing a boulder up a hill) is about potential exhaustion at repeatedly doing the one “most efficient” thing to the point that you’re not taking 60 seconds of mental refreshment. Psychological viability is the missing element here, causing us to intuitively sense that the proposal isn’t actually best, utility calculation be as it may (the actual calc would not have such problems).