Libertarian blogger Jonathan Rowe has suggested that slavery and capital punishment were not abolished in America as a result of Biblical Christianity as much as by liberal Christianity.
Never mind that liberalism is an entirely different non-Christian religion, it may be true as a matter of history that the unitarian terrorists had more to do with ending slavery than Biblical proof-texters did. They certainly had more to do with it than Bible-quoters like Robert L. Dabney.
But the silence of Bible-thumpers does not prove the silence of the Bible itself. James B. Jordan and Gary North have both written volumes on how the Bible expressly moved humanity away from slavery. Gary DeMar has summarized their work.
The abolition of capital punishment is yet future, but it too can rest squarely on Biblical texts, and not a post-Christian world-and-life view, as I argue here.