That would be fine if humans simply walked around consuming plants that would have otherwise decomposed and there were no other resources associated with food p

That would be fine if humans simply walked around consuming plants that would have otherwise decomposed and there were no other resources associated with food production. Unfortunately, agriculture is a major driver of deforestation (and forests are excellent at actually sequestering carbon in the ground). It also requires trucks, boats, and planes to haul supplies to farms, work the land, move water around, and transport the produce to stores. You have processing and packaging that rely on fossil resources (paper, plastic, metal cans...) That doesn't even touch on the impact of meat production, which is several times worse for the environment. Food consumption is absolutely not carbon neutral. You're far better off taking public transportation to work (if available) than walking or riding a bike, if you care about the environment.