“Because the bottom line is this: regular consumption of meat and fish just isn’t sustainable. [… If] everyone on the planet ate that way starting … NOW! … we’d be out of land, food, animals, everything in about 2 minutes. It’s really as simple as that.”
Let’s grant that, if everyone on the planet started eating certain kinds of meat or fish all at once, it would not be sustainable. How does that affect whether a given person should eat meat at some point in time? It seems irrelevant, because the given person isn’t going to cause – by their act of eating – everyone else to act in the same way.
Consider an analogy: you might be sitting in a chair right now. If everyone on the planet sat in that chair starting now, almost all of them would be crushed to death. Therefore, should you not sit in the chair?
Obviously, there’s been a mistake in logic somewhere if that’s your conclusion. What’s relevant in considering the morality of an action can’t be what would happen if everyone did it.