> Basically you are saying that, because of a quirk in human psychology, the only way to get people to donate, over the long term, a portion of their income, derived from them doing jobs they are much more productive at than building houses, to building houses, is to engage them by having them build a house themselves first.
Having people engage in a process isn't just for personal fulfillment of "morally incompetent" people: it also serves as due diligence.
Trust is a big factor of deciding where you want to donate your money. Having walked through the process as a volunteer, you have a much clearer picture of how your donations are spent, and yes you are more likely to donate.
Trust has to be earned one way or another.
Piggybacking on this home building example with an extreme example: how would you feel if you donated for years to some non profit which builds houses, but later learned that child labor is used to build those as well as cheap, structurally unsound materials, with the non profit CEO pocketing millions?