[pcstl]

There are a lot of hidden assumptions here.

One of them being that protein-dense foods always has a greater impact on the environment than other foodstuffs. There are plenty of vegetarian or even vegan bodybuilders, and we know how to isolate protein from vegetables. Pulses are protein-rich, if you don't want to eat isolated proteins.

The second one is that a muscular body will always require more energy than a non-muscular body. While muscle does have higher calorie requirements than most other kinds of tissue, most fit people actually eat less calories (and better quality calories) than unfit people, due to being used to keeping their diet under control.

The final one is that the only thing one might want to do with their life is their job. Even if you work a desk job, that doesn't mean you won't want to be physically active in your off time.