[throwaway20201]

Your logic breaks down when you consider the fact that humans will never consume as much plant matter or water as livestock.

In fact, the creation of meat is a wasteful process, requiring up to 25kg of grain and 15,000 litres of water to produce 1kg of steak. [1]

1: http://waterfootprint.org/media/downloads/Report-48-WaterFoo...