Tell them what? that we've grown so fat and stupid on the abundance the earth provides that we can't properly manage it and will probably cause millions undue suffering because we don't want to reduce our meat consumption to less than 250lbs per year despite it being easily possible?
Heh, I eat a lot of meat and still less than 250lbs per year. That's a perfectly fine number. The parent was saying that zero was the right number. Zero is really not the right number for much of the current human population. We shall see what happens in the future.
I'm with you that the collective we is fat and stupid and would go further than our various systems and patterns solve for predatory behavior against both humans and non-humans leading to those outcomes, and it is super unfortunate.
0 is a great number for rich countries to aspire to. Without some sort of massive crisis (which we're heading towards globally) it would probably take at least 100 years to even halve the current consumption levels. It took roughly 100 years to go from an average of 10lbs of chicken consumption per year (1920) to the current 70lb average (2020). Chicken is really where all the growth for meat consumption has come from.
Beef has been fairly steady per capita, and has decreased from its height a few decades ago — but the population keeps rising so it can't continue like this.