I am adding the following as a compliment to the above post on why Baptists are still discussing their origins. I just finished reading The Historiography of Baptist Origins in Selected Southern Baptist Historians: William Heth Whitsitt, John Tyler Christian, and Albert Henry Newman, a PhD dissertation by Donald Alan Cureton. I think the following is apropos. Each man in Cureton's study is representative of a different view of Baptist origins: Whitsitt - English Separatism; Christian - Succession; Newman - Spiritual kinship. What Donald Cureton describes concerning these men as "three realms of diversity" is probably generally true of others.
"...differing historical methods, superimposed biases, and divergent definitions of Baptists." (p. 166)