> A better one, like you mention, is rice - again a crop with substantially worse carbon impact than chicken.

Do you have a source for that? The data at [0] indicates that chicken is about 50% worse than rice in terms of CO2e per Calorie. In fact, chicken is worse than every vegan food listed there except for broccoli, which has very few Calories to begin with.

[0] https://sustainability.stackexchange.com/questions/5883/why-...