The point I think you are missing is choice.
For most of history (and for most people in the world today) if they want to get enough nutrition to survive they eat meat, that's why we're evolutionarily equipped for it. Our own survival tends to come before the pain and death of animals that we have control over. I get that, and under the same conditions I would kill and eat a pig. Frankly in extremis I might eat a person.
The difference is that in our hermetically sealed, mollycoddled, western lives we can get all the nutrition we need without the pain and death of other animals (other than the poor sods breaking their backs in the production of veggie food of course). Some of us make that choice. You can argue about what constitutes morality until you are blue in the face, we all draw lines in arbitrary places about the stuff we think is right and wrong.
I have to wonder why you are so angry about this. Nobody is threatening to take your steak away. I think the point that some people are making is simply that if you care about how an animal lives or dies, which Zuckerburg seems to be claiming he does, you could simply choose not to eat them.