What was the main argument that southerners made in defense of slavery? a) the right to own slaves was guaranteed under the first amendment to the u. s. constitution. b) if the founding fathers had slaves, it should be ok for people who lived in the 1850s to have slaves. c) it was up to the states to deal with the use of slavery because it was provided for in the constitution. d) the future of american economic development depended upon the continued existence of the southern system of slavery.