A non-diminishing-returns altruist would hit a point where the utility of spending a marginal resource on a "selfish" purpose dips below the best use of that resource for an "altruistic" purpose. Every single marginal resource after that should go toward altruistic purposes as well. Why? Because for anyone with non-astronomical resources, there is effectively an endless supply of altruistic options that all provide effectively the same degree of benefit to the recipient. The non-diminishing-returns altruist would increase altru... (read more)
When I say that I am selfish, I mean to express that I think the best model for "altruism" is that of a good consumed much like any other. I consume it for my personal enjoyment, not in proportion to the benefit received by the recipient. And, ceteris paribus, with a declining marginal utility as quantity consumed increases.
In my eyes, a "true" altruist would value the 1000th meal provided to a starving third-worlder on par with the 1st one provided, given that the beneficiaries valued the meals similarly. Nobody behaves that way. Altru... (read more)