I do think you are oversimplifying by a large amount, not all food contains the same things, and very few plants do contain proteins, some animals can metabolize the proteins they need from what they find in random leaves but humans, like many omnivorous and carnivorous animals, can't, we need to find those protein somewhere else, and the most space and cost efficient source of that for millennia has been meat, now with newer advances soy and mushrooms and some other plants or insects may be a better option.
But it is not as simple as vegies > meat because more biomass, of course there is more biomass, carnivorous depends on meat, so you need maybe 100 herbivorous to sustain a carnivorous of similar size, same goes for plant vs herbivorous.
I am pretty sure that you want to do the right thing teaching the world that meat is bad, but you do look a bit stupid without any arguments.
Pretty much everyone in developed countries eat way too much meat, the recommended amount last time i checked was 50 to 100g per day, where a steak usually weighs about 200g and peoples eat 2 per day... maybe that should be a start, dividing by 4 to 8 the consumption of meat would have a considerable impact already.
