I have a vivid memory of a young boy throwing trash out the window of a bus in Mexico. Piece by piece, his mother handed him a plastic shopping bag, a food wrapper, a Styrofoam plate, a fork, a plastic water bottle. Each item twirled briefly in the air before settling on the side of the road, amidst piles of colorful and stinking detritus. The little boy squealed with delight. His mother clapped her hands. I sat silently next to them, angry and resentful, feeling powerless to do anything about it.