1) Advocate 2) Advocator 3) An advocate of secessionism 4) Exponent 5) Proponent 1) Rebel 
• (n.) One who holds to the belief that a State has the right to separate from the Union at its will. • (n.) One who upholds secession.
Se·ces'sion·ist noun 1. One who upholds secession. 2. (U.S. Hist.) One who holds to the belief that a State has the right to separate from the Union at its will. 
[n] - an advocate of secessionism
noun an advocate of secessionism