You're right, of course, but it's not nearly as easy to say succinctly with a clever quip to make a point. The civil war started because states suceded because Lincoln was elected. They did it because there was a gradual progression of laws being enacted with the goal of eventual extinction of slavery in the US. Lincoln's win guaranteed that this was going to continue past some intolerable point for the South and so, secession.

It's a bit like admonishing the protestors for protesting TTIP before it was enacted. Probably could have chosen slightly more accurate words, but my point was still made.