Would anyone of average intelligence who wants to do as much good as possible fail flagrantly in giving where it maximizes welfare? Why then the drastic difference between personal buying and donation? Someone planning an Arctic trip will not make the contemplated mistakes, which is why you used personal buying to contrast with donation practices. Whether the desire to benefit mankind is powered by warm fuzzies or some other expression of altruistic motivation, if contributors were human-welfare maximizers they would do a lot better at maximizing welfare. People aren't that irrational!

Donations have little to do with welfare maximization and warm fuzzies. They primarily function as a signaling device. Isn't that obvious?