I don't know what's so hard to get. If you took land used for meat and turned it over to food processing and made humanity primarily vegetarian (maintaining smaller animal populations for food and diverstity) you could make up for any loss to ethanol or oil.
The problem is is that ethanol (and any grown plant based alt fuels) results in a net energy loss, ie you get less energy out than you put in. Same with farming from animals, however the latter is far more institutionalized than the former.
Hydrogen cells are far more energy efficient and energy rich than ethanol or electric cars.
Man is not a vegetarian species. We are omnivores, without meat in our diet you have to have some very specific types of non meat food sources or vitamins to replace what you lose by not eating meat.