Huh? I'm a big proponent of eliminating agrochemicals, but you've set up a huge straw man here: No one is arguing that agrochemicals are "necessary" in the sense that agriculture is impossible without it (indeed, millennia of experience prove otherwise). Rather, the rationale is that they allow us to increase productivity for the same input of acreage and man-hours.
I'm not saying that agrochemical proponents are right (I've heard that crop rotation is as good or better than synthetic fertilizers, though it's hard to argue against the labor efficiencies of huge tractors and lots of pest/herbicides), but the simple fact that agriculture is possible without agrochemicals doesn't disprove the argument that it might be better with them.
