However, most people in first world countries are in this situation of opportunity to do extreme good in exchange for a relatively small sacrifice, but most don't do it, mainly due to ignorance of a tractable way in which to do it.

If you care about impact, our intuitions regarding goodness just kind of suck: When you ask most people to picture someone environmentally conscious they will conjure up an image of a garden, a detached home, maybe an electric car, buying local, etc...