Ubik, you're committing a bit of a non-sequitor here...and Leanan is kind of at fault for bringing up a point that is largely orthogonal to your main point (50% reduction in meat production). It's a sad day when two people who agree waste their time arguing.

Your point about consuming more grain directly, rather than via livestock, is a fair one. The same goes for your point that meat consumption should be cut in half. But you are failing to address Leanan's point that livestock can convert largely indigestable stuff (ie. grass, legumes, shrubs, and brush) to human-digestable food (meat). And this can all be done with a bare minimum of labour or fossil fuels as input (see the book above).

My understanding is that 70% of grain produced in the US is fed to livestock (source: Joel Salatin's excellent, but unfortunately named, You Can Farm). This is absurd, especially when you realize that cattle, sheep, and goats are quite inept at digesting grain (but this is not true of pigs, chicken, and several varieties of farmed fish). Cultivating land so that you can feed livestock something that they aren't particularly good at digesting is a type of lunacy that will end with increasing transportation fuel costs. It is my belief that meat production would only fall slightly if land used to grow grain was converted to pasture for ruminant livestock to graze directly. Mr. Logsdon actually makes the argument that this change could bring an increase in per-acre production, and all with much less fuel consumption.

As for water, all the water consumed by a livestock animal is not wasted. With pastured livestock, much of it spread onto pasture as urine. In effect, you get some irrigation for free just by watering your cattle. The same goes for the protein, carbohydrates, and fiber. The pies can either be left for the benefit of the pasture, or used for vegetable production.