Hi BN! Thanks for your question
You're right that one of the ways to attack a basic causal conclusion is to show that the effect happens when the cause is not present!
However, the stimulus for this question does not rely on causal reasoning, so showing that the effect happens without the cause will not weaken this argument. Instead, the journalist is relying on conditional reasoning in making their argument; the use of words like "when" and "whenever" serve as clues that conditional reasoning is present.
The issue with answer choice (A) is that the journalist's argument is about situations in which judges don't maintain strict control over their courtrooms. Answer choice (A) then tells us something about situations in which judges do maintain this control. But knowing about situations in which judges maintain this control doesn't weaken whether lawyers engaging in obstructive behavior from a lack of strict control affects the validity of the jury's verdict.
Another way to see this is to imagine if you replied to the journalist's argument by offering him answer choice (A) and how the journalist would respond in turn. In this case, the journalist would respond to you as follows: "My argument is about the situations in which the judges are not strict. Just because there are sometimes incorrect verdicts when judges are strict in controlling the behaviors of lawyers doesn't mean that there aren't also incorrect verdicts when judges are not strict."
To sum up, be careful not to pick an answer choice that is a classic way to weaken a basic causal argument when the stimulus does not use causal reasoning. In this case, we could rely on keywords such as "when" and "whenever" to determine that conditional reasoning is used, not causal reasoning.
I hope this helps, and let me know if you have any other questions!