The bulk of the food cows are eating is unfit for human consumption. You couldn't feed it to people even if you wanted to. Our digestive system is completely different and can't be "upgraded" to work like that of a cow.
Calories are not all equals, otherwise we could just feast on corn sugar all day and be healthy.
If you want to be a vegan because you feel sad thinking about animals being slaughtered or because you have a craving for foliage, knock yourself out, but stop peddling that bullshit that's been around since the hippies.
Our digestive system can't digest corn and soy? That's what cows are fed in industrial agriculture. Get your facts straight and ease back on your venomous hate.