The real issue with animal-based high-protein food choices is not about your individual health, nor is nutritional deficits. Assuming that you are in fact eating a healthy, nutritionally complete high-protein, high-satiety diet.
The issue is the planetary impact and indirect harm to all human beings.
Think of Earth as an almost closed-off circular system with a finite capacity to handle annual pollution, natural resource drain, natural loss, and imbalances.
Now, take roughly 9 billion humans and add our environmental impact together, and you are left with the mathematical reason why sustainability matters when we discuss healthy food habits and our individual nutritional intake.
Case A.
Beef requires roughly 20 times more land than nuts, and 35 times more than grains to produce the same amount of edible protein.