Yes they did fight for the right for slavery to stay legal in their states, but they were totally against state’s rights when it came to other aspects of slavery. The fugitive slave law and other acts by the federal government attempted to impose slavery rights in northern states. It’s not that the southern states had some high minded principle of the autonomy of states or something. Only when it would result in something they wanted, like slavery. Otherwise they were happy to discard “states’ rights.”