Choice D is the best answer. In Passage 1, Lincoln uses abolitionism solely as an example to illustrate the argument he is making about heeding the law: "In any case that arises, as for instance, the promulgation of abolitionism, one of two positions is necessarily true" (lines 37-39). In Passage 2, Thoreau does the same thing by noting that "those who call themselves Abolitionists should at once effectually withdraw their support... from the government" (lines 79-82). Although Lincoln and Thoreau use the cause of abolitionism to argue different points, a commonality they share is that neither embraces the cause personally in the passage; Lincoln simply uses it as an example ("as for instance") while Thoreau specifically talks of other people "who call themselves Abolitionists."
Choice A is incorrect because in Passage 1, Lincoln argues against drastic action, saying that even in the case of abolitionism, such a response is not "necessary, justifiable, or excusable" (line 44). Choice B is incorrect because it's not accurate to say abolitionism was central to the arguments, only that each used that subject as an example. Choice C is incorrect because neither Lincoln nor Thoreau offers an opinion about whether or not abolitionism will gain widespread acceptance, instead they incorporate it only as an example in their discussions of just and unjust laws.