Leads to wrong conclusion. (A) is designed to lead to a conclusion that certain laws shouldn’t be part of a legal system. But the conclusion we’re trying to support isn’t about whether certain laws should be in a legal system. It’s about whether a certain thing should be a factor in how judges decide to punish.

Mitigating punishment on the basis of motives involves making punishment more lenient if someone had a good motive. (B) establishes that it’s better to punish someone too severely, at risk of not taking into account their good motive, than it would be to mistakenly think someone had a good motive and give a mistakenly too lenient punishment. In other words, even though we might punish someone more than they deserve, that’s better than letting someone trick us into giving them a more lenient punishment because we thought they had a good motive. This is the underlying principle guiding the author’s recommendation that we shouldn’t mitigate punishment based on motives.

Leads to wrong conclusion. (C) concerns whether an action should be legal or not. But the argument doesn’t concern whether actions should be legal. It’s about whether a judge should take into account motives when determining punishment. The argument isn’t trying to assert that it should be legal or illegal for a judge to take into account motives.

Leads to wrong conclusion. (D) concerns whether a law should be enacted. But the argument doesn’t concern whether a law should be enacted. It’s about whether a judge should take into account motives when determining punishment.

Leads to wrong conclusion. (E) concerns whether a legal system should be adopted. But the argument doesn’t concern whether a legal system should be adopted. It’s about whether a judge should take into account motives when determining punishment.