(A) doesn’t tell me why we “should not” do something. Sure, maybe human intervention reduces biological diversity...but is that something we should care about? We don’t know.

(B) isolates protection of forests and their ecosystems as the only “legitimate” reason for trying to prevent or control forest fires. In other words, no other consideration should matter when deciding whether to prevent/control forest fires. And, since we know from the premise that forest fires are good for the protection of forests, (B) implies that we should not prevent/control fires.

We’re trying to conclude that we shouldn’t systematically prevent/control forest fires. (C) goes in the opposite direction.

(D) doesn’t establish that we shouldn’t try to prevent/control fires. How humans perceive forests doesn’t prove anything about what humans should not do.

(E) concerns threats to an ecosystem by insects or other predators. But we have no reason to think this is related to threats posed by forest fires. What humans should do in response to threats by insects or other predators does not prove what they should do in response to forest fires.