1 person requires 1 acre of veggies to live for one year.
400mil in the US, 400million to sustain current population level, add in acres for ethanol production, which the added amount in 1 acre of land for E10 puts 72,000miles on the road. Lower for E85 & E100 (obviously). Also, you want to make extra incase crops fail due to lack of water, pests, or any other unseen disaster.
For some crops, it takes hands on in order to pick them for consumption. So, we'll be needing a lot of people willing to pick food all over... lets say 750million acres between the ethanol, overage & initial crop to support 400mil. That's a lot of workers.
Now, how much land is available in the US's lower 48? 1.9billion. We're almost halfway there. Then take in account the land which is used for housing, businesses, manufacturing, industial areas, etc. Then, throw in land which needs to be either terraformed to support the goal of growing crops, as well as land which cannot be used because it's covered by water, rocks, or any other means which cannot be planted on. National Parks, federal land, private land, etc. It'd drive land prices way up.
A cow for 1 year costs around 300 to 400 bucks. Cow droppings are used as fertilizer and in growing veggies, especially with doing organic, they spread it. A heard can be monitored by a few ranchers at once on horses & graze their heards on land which is most of the time unsuitable for crops. When animals are slaughtered (unless in Halaa or Kosher ways) are stunned with high electricity so they are unaware of what happens. They aren't crammed in pens their whole life. A stressful animal doesnt yeild good taste so they're given good treatment. PETA videos usually show that one guy who is about to lose his job for being a degenerate doing something no one agrees with.
So, why eat meat? It's there as well. If you don't like meat, go eat veggies. It's really none of your business what anyone else chooses to eat.