@Michael Raburn
(I've cleaned up this post substantially)
The basic point I'm arguing here is that emancipation from slavery is necessarily an extension of human rights. I think that this is a definitional question before it is even a historical question. What we mean by emancipation must be an extension of human rights, if "emancipation" is to mean what we normally mean by it. To suggest that emancipation, insofar as it happened, didn't involve human rights is a contradiction in terms, just like "we need friendship, not rights" is a contradiction in terms. (I'd also note that the definition of modern human rights as secular rights is in dispute here. See Wolterstorff.) And so suggesting that "human rights didn't effect an end of slavery," is like saying, "hydrogen doesn't effect water." It is a basic category mistake, which suggests some basic empirical mistakes may also be going on as well. (As does a statement like this: We need water, not hydrogen!)
Still, let's discuss the actual history of opposition to slavery, prior to emancipation, as well. Insofar as revival gave rise to abolitionism, this was an opposition that integrated human rights discourse at a basic level...and there were a lot of people who were part of this movement who weren't influenced by revivalism in any kind of obvious way. For example, Thomas Paine was hardly a revivalist...he was about as secular and humanist as they came, and he was also an advocate of human rights and an early opponent of slavery. Moving on from there, Frederick Douglass was hardly a critic of human rights or natural law, although his vision was deeply religious. http://plato.stanford.edu/entries/frederick-douglass/#NatLaw. In their embrace of human rights, I don't think they were exceptional abolitionists...they were typical. And in possessing divergent religious views, they were also "typical" of abolitionism. What really united abolitionists was opposition to slavery, and across the spectrum, this opposition was clearly and consistently connected to human rights.
So at minimum, the historical picture is way more complicated than "secular modernists who appealed to secular human rights were the pro-slavery people (like Locke!), and Christian revivalists who opposed secular human rights were the anti-slavery people." I'm not even confident that these tropes reflect general trends, let alone a satisfying total account of events. Even Locke's own position on slavery is highly ambiguous, and a matter of dispute...and his religious views are also, similarly, highly debatable. For example, some of Locke's arguments that get him flagged as a "deist" are basically Thomistic arguments. The nexus of "Locke-secularism-humanism-deism-human rights-slavery," is itself highly contested and rather dubious at each point...even before we go on to ask things like, "How much influence did Locke even have on the American Revolution?" Once you start asking whether abolitionists were critics of human rights, or advocates for them, I think the narrative implied by the claim that "human rights didn't bring an end to slavery," falls apart. Human rights were a big part of what people in, and cooperating with, the black churches were advocating. To set them against each other is a total false dichotomy.
But more narrowly, of course, I'm not saying that "human rights ended slavery." I don't think "human rights" are a historical agent. Rather, the end of slavery was itself a recognition of human rights. This is what it was, as a matter of fact, and it was also how the people who enacted it understood it. This was accomplished through a historical process in which the action of people, empowered by the Holy Spirit, played an important role. And all truth is God's truth, so God is the ultimate author of any good that was accomplished at all. I believe that God is the ultimate author of human rights, independent of any causal role played by revivalism. (God's actions are certainly not constrained to revivalism!)
So to say, "the founding documents were steeped in just that sort of Lockean rights language..." doesn't really reflect the complex dynamics here. Rights language was also integral to abolitionism. Your arguments here seem to imply that it wasn't. If that's what you're saying, I think this gets the history wrong.
At any rate, my illustration of Old South rhetoric was simply intended as an illustration of how the appeal to love and friendship, paired with a critique of human rights, actually worked in Old South apologetics. None of the point I was making with that example depends on these broader historical questions. (Although they are germane to the broader discussion!) Instead, the illustration is designed to help us discern why those kinds of arguments seem appealing (to those who don't want change), mirror some of what I'm hearing now, and are total b.s. My point is that "you need Christian friendship and love, not human rights," was, precisely, one of the arguments used to justify slavery. My critique of this argument is that it represents a misunderstanding of friendship and love, which creates a smokescreen justifying the violation of rights. A proper understanding of love must include respect for human rights.