This is the worst analogy I've ever heard.

The fact meat is more energetically dense than plants doesn't matter, as vegetable products can still be processed, baked, brewed, etc, into forms that are denser and easier for human consumption. If it were impossible to eat that many calories from vegetable products only, vegans would die.

You shouldn't be thinking about how much calories 1kg of the substance contains, but how much calories can be created in one acre where the substance is grown. If you grow 100,000 kcal of beef, then you had to grow 100,000 kcal of dry corn somewhere else because of conservation of energy. In practice it's even more than 100,000 because cows can't absorb with 100% efficiency. Living beings are terrible heat engines—a number that I've often see biologists throw around is 10%. So to produce those 100,000 calories in the form of beef you had to produce 1,000,000 calories of corn to actually feed the cows. If people just ate the corn directly, you would've been able to feed 10 times more people.

So yeah, as much as meat is delicious, it's a terribly wasteful use of land. The fact you need to eat a big salad as oppose to a small steak to get the same number of calories is a minor inconvenience.

the carbon released from the animal came out of the air not too long ago

No, the methane is produced in the cow's digestive track by combining CO2 with H+ and free electrons; it;s not methane that existed before in the atmosphere. You lose a CO2 molecule and in return you get a brand new CH4 molecule. Methane is much potent in heating the planet than CO2, so you're worse off.

methane naturally breaks apart over a short period of time

Methane isn't an unstable molecule, it doesn't spontaneously break down. It can be removed from the atmosphere by free OH- radicals, but OH- doesn't magically appear. If there's too much methane, there won't be enough OH- to remove it, and the atmospheric concentration of methane will rise.

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