Yeah, looking at it from the perspective she wrote, it seems ridiculous. It is an "industry", wrapped in a non-profit, save-the-world PR shroud, that caters to educated, Westerners who can afford to travel overseas. People feel good when they do good. Whether they other side perceives it as good, sometimes it is not clear.
One can ask, is it better if these "unskilled" people never left home? Maybe even with all the seeming waste and incompetence, it keeps people engaged. I suspect most of them would not have just taken the money for that plane ticket, and handed that check to a NGO that knows better how to spend it, and could build 10 libraries for all that money. But I am afraid it is either "send the volunteers and keep them engaged somehow" vs "don't send the volunteers at all and say goodbye to that money and resources".
People like to help others, people like to tell stories, like to have adventures. These trips cater to that aspect. Do people in Africa feel better knowing that foreigners want to come in and at least try to slap a brick on top of another even if they don't know how? I see a lot of criticism of this here, and rationally I agree, but I also feel there is a bit more too it and I personally am on the fence whether this is good thing or not.