We now have 8 billion people. Who all want good food, a big house, personal transportation, travel, smartphones and so on. And last but not least they want kids, too (which they claim is a "human right").
You can either keep telling yourself that this is fine and can go on forever, because science will magic the shit out of everything (or the flying spaghetti monster or space aliens will save us from ourselves), or you can realize that it is not sustainable.
See, you say 1 billion cows are a problem for the planet because they eat so much and produce so much methane, and the cow population should be reduced. But you have no problem with 8 billion humans?