Beef is a product made from cows. Cows require land, food, water, and infrastructure. Producing beef leads to the destruction of ecosystems, like the Amazon Rainforest [1]. By consuming beef, you are contributing to this phenomenon the article discusses. The emissions from your car, similarly, contribute to climate change and the destruction that goes with it as well. The lifestyle one chooses to lead, the products one consumes, and the decisions a person makes are all very much factors in the reduction of animal populations.
I'm starting to believe that you aren't arguing in good faith, in part because your statements are just thrown out there without any evidence or citation. Sure, a pound of beef or chicken contains more protein or calories than a pound of vegetables. But that's a nonsensical and misleading claim - many more pounds of vegetables went into producing that pound of beef and chicken. Many of those calories, by the way, were exhausted by the metabolic processes of those animals too. A much more efficient utilization of resources would involve just using those vegetable calories directly.
[1] http://journals.sagepub.com/doi/full/10.1177/194008291300600...