alt Hacker NewsNo, you are not getting what people are trying to tell you: growing the food for the extra 7 billion completely cancels out the co2 emitted from the 7 billion pairs of lungs. We know that because the C in that emitted CO2 all comes from food eaten by the person at some point in the person's life.
I think you might be missing the point too. Yes, the carbon in the food we eat is where the carbon in our breath comes from. But the carbon that we used to get the ingredients in that food didn't certainly come from the atmosphere (e.g. half of the nitrogen used in agriculture comes from fossil fuels). You can't be a perfectly optimal salad eating machine. One of your fellow humans will ruin the equation the moment they buy produce from the modern supply chain.