This is the first of two articles dealing with the most inflammatory domestic issue now before the country. HERBERT RAVENEL SASS, author and long-time contributor to the Atlantic, presents the fundamental case for the white South. A native of Charleston, South Carolina, an independent, and an Episcopalian, Mr. Sass is imbued with a tradition which he believes is based on unchanging truth. His argument goes to the very heart of the controversy: Would integrated schools lead to mixed blood?