Hi Henry,
Answer choice (D) discusses the likelihood of a decision maker deciding in favor of ideas in which they do not actually believe. Sometimes these answer choices can be tricky to decipher, but what answer choice (D) is saying is specific to the decision makers, as opposed to any other people who might be observing the decision-making process.
Part of the reason we know this is because answer choice (D) does not mention other people's perspectives or the impression they get from hearing a certain decision maker's argument, rather, it discusses the likelihood of a decision maker deciding for or against an idea. In answer choice (D), the phrase "makes it likely" refers to how the process of decision making (in this case, the process from the stimulus is advocating for ideas they do not believe in order to see if their advisers have reservations about the idea that are similar to their own) increases the chances that the decision maker ultimately decides in favor of an idea they do not believe in.
Something that might be helpful to consider is the Fact Test, since this is a Must Be True question. Parts of answer choice (D) cannot be proven by referring to the facts in the stimulus. For example, answer choice (D) says they will "frequently decide in favor of ideas in which they do not believe," but the frequency of such decisions is not mentioned in the stimulus. We can use this same line of thinking to understand why you're noticing that people are reading that decision makers actually decide that way, since the answer choice discusses the actual likelihood of a final decision in favor of a type of idea.
Hope that helps!
-Kate