[griffinmahon]

One of their counter-arguments to your second sentence is that if you, the ethically-minded person who will donate a significant portion of your income, aren't in that position at the potentially exploitative job, odds are someone else will be who isn't ethically-minded. On the other hand, if you were to go work aid on the ground in Africa, it's likely that you, who maybe has a valuable skill-set capable of earning more, could be replaced by another person who wants to work in aid.