>We could stop using huge amounts of oil to create the huge amounts of food required to feed cattle that become our beef meat.

Technically, this would improve food yields relative to fertilizer utilization, but it does nothing to deal with fossil fuels for farm equipment, transport, processing, refrigeration, etc - and you would STILL need massive amounts of fertilizer to feed the existing population. The carrying capacity of the earth without advanced fertilizers is probably in the neighborhood of 3 to 4 billion people.

It's also politically untenable, of course. I think that you will find that the majority of the population is simply not willing to give up meat in their diets. A solution that nobody is able to implement isn't really much of a solution.