Mainstream Baptists believe in

 Religious Liberty

and the Separation of Church and State

George W. Truett expressed Baptist beliefs most succinctly:

"Religious Liberty is the nursing mother of all liberty.  Without it all other forms of liberty must soon wither and die.  The Baptists grasped this conception of liberty in its full-orbed glory, from the very beginning.  Their contention has been, is now, and must ever be, that it is the God-given and indefeasible right of every human being, to worship God or not, according to the dictates of his conscience; and, as long as he does not infringe on the rights of others, he is to be held accountable to God alone, for all his religious beliefs and practices."

Dr. Truett was pastor of First Baptist Church of Dallas, TX 1897-1944, president of the Southern Baptist Convention 1927-1929, and president of the Baptist World Alliance 1934-1935.  The quotation is from Truett's famous sermon, "Baptists and Religious Liberty," preached on May 16, 1920 to 15,000 people from the steps of the U.S. Capitol in Washington, D.C.