I appreciate your specificity there — you leave room for the fact that there were other issues at hand, besides slavery, especially for the majority non-slave-owning class that fought and bled in the war. The South certainly seceded for the cause of slavery, but the North, instead of solving slavery peacefully the way every other western nation had, decided to go to war to preserve the Union and its economic dominance over the South.
So yes, sympathy for their cause and point of view I think is important — both North and South — especially since there were a great many Northerners who were just as, if not more racist (including northern slave owners whose slaves were not emancipated with the Emancipation Proclamation). Lincoln himself was an unabashed racist, and it truly is only due to the noble acts of northern abolitionists that his war was co-opted to free the slaves.
As for Leviticus, and Christian dogma, there is simply no comparison to sharia. In fact, Christianity explicitly repudiates the Old Testament with Jesus Christ — it’s literally God’s “New Deal”, where Jesus’s death on the cross was a sufficient sacrifice to atone for all the sins of man (including homosexuality), now and forever. The fact that an alarming number of sharia supporting muslims believe that homosexuality should be punished by death, according to the most extensive Pew polls done, should clearly indicate the severity of the problem.
Slavery is wrong. Seceding to preserve slavery is wrong. Fighting to destroy slavery is wrong, when it could be resolved peacefully for less cost (and it was, throughout the western world). Do you disagree?
Or should we be planning invasions of islamic and african nations who still practice slavery? Maybe our cause against ISIS and Boko Haram could simply be re-branded as the liberation of the slaves they hold and auction?
