(D) is a tempting answer choice. It is ultimately incorrect because it ignores the conclusion of the passage (roughly lines 44-54). The passage describes why it is hard to judge risk because there are lots of considerations that factor into whether it was a voluntary risk. At the end, the passage then recommends that policy judgments should be guided by the factors underneath a voluntariness determination. Answer (D) just says that making these decisions are difficult, but does not talk about the recommendation.
(B) rephrases the final recommendation of the passage (lines 44-54). The passage says that the "government should attempt to save as many lives" as possible (lines 46-47) and that departures from this should only be done by looking at the factors underlying voluntariness (lines 52-54). Answer B states this by saying that decisions should first and foremost be about saving lives. It's tricky because it says not to focus on voluntariness. While the passage talks about voluntariness a lot, in the end the recommendation is to save as many lives as possible (46-47) and this is reflected in B.
