If anything, the opposite is true. You can read the declarations of secession for the southern states; e.g. see South Carolina's [1]. They seceded to protect the institution of slavery. Surely some people had other reasons to support secession, but this is the primary one. Decades after the war ended, there was a push to deemphasize slavery as a cause for the war for reasons of propaganda and nostalgia.

[1] https://avalon.law.yale.edu/19th_century/csa_scarsec.asp