What if that line starts very slowly flattening out? Is that enough evidence?
you'd have to show the causal link between vegans existing and the production flattening. what if it's just that we run out of agricultural land, or a meteor strikes a major production region? we need to know what actually causes the change in the graph, not simply speculate that it could be buying beans.
When we run out of land, won't we have to replace land used for meat production for land for plant production so we can continue feeding an expanding world?