Explanation :
The ethicist's core argument: Meat production is inefficient (16:1 grain-to-meat ratio), meat is only marginally more nutritious, and with grain scarcity + population growth, eating meat will soon waste resources that could feed more people, making it immoral.
Gap/Assumption: The argument hinges on all (or most) meat production relying on grain-fed animals, exacerbating the global grain shortage.
B weakens this most seriously by introducing an alternative: Many animals (like cattle/sheep) can be grass-fed on non-arable land that couldn't grow grain anyway. This means meat consumption doesn't always compete for the same limited grain resources—undermining the inefficiency claim and the moral urgency tied to scarcity. It's a direct attack on the causal link between meat-eating and grain waste.
Why Not the Others?
A: This is about consumer preference/willingness to pay—irrelevant to the moral/resource argument (it might even strengthen the "people will keep doing it anyway" angle, but doesn't touch the ethics of scarcity).
C: Suggests grain diets can be nutritionally fine with supplements, which mildly questions the nutrition premise but doesn't address the core inefficiency or scarcity issue (you could still feed more people with the grain used for meat).
D: Talks about farmland loss to suburbs, offering a partial solution to scarcity—but it strengthens the problem's existence rather than weakening the meat-eating blame.
E: Reinforces the nutrition gap (grain alone isn't enough), which actually supports the argument that meat provides value (even if inefficient).