Moderation. I can tell you right now that the farming industry would have a much tougher time if everyone was vegan. Crop growing isn't as simple as throwing seed on the ground and harvesting. You have to consider soil nutrients, irrigation, harvesting, pests, and a host of other problems. You can shove more meat into one area to grow then you can plants. Farmers would have to expand their crops basically meaning throwing local wildlife out of their homes. Harvesting also has its casualties. A lot of animals get killed by harvesting equipment then you think. More vegans=morehavesting=more animals killed.