Answer choice B vs C

I agree that's a clear flaw of the argument, the author clearly seems to assume that farmers want to preserve their way of life, but we have no idea if that's true. That said, I think that's clearly a social concern. Dealing with issues of identity lifestyle and social organization are social matters, regardless of whether a decision on such a matter is good or bad for the group at hand. The argument clearly involves deciding that this social concern outweighs an economic one. The issue with B is that it goes way too far. While the argument conforms to principle that producers can sometimes outweigh consumers, we have no idea if it conforms to the principle that this is always true.

I understand B goes very far. Would it have been right if the question stem "which principle would most strength the recommendation?" Since it says "conform" I should've matched the strength

Yeah, I think B would strengthen the argument. Illustration questions are kinda weird, and keeping them separate from principle strengthen questions is pretty important.