Out in front while we talked, the younger Bates children were playing with the neighboring Negro youngsters. Here was another one of those ironic touches which
life, oblivious of man's ways, gives so often. If the nine youths on the freight car had
been white, there would have been no Scottsboro case. The issue at stake was that of
the inviolable separation of black men from white women. No chance to remind
negroes in terrible fashion that white women are farther away from them than the stars
must be allowed to slip past. The challenge flung to the Negro race in the Scottsboro
case was Ruby Bates, and another like her. Ruby, a girl whom life had forced down to
equality with Negroes in violation of all the upholders of white supremacy were
shouting. As a symbol of the Untouchable White Woman, the Whites held high-
Ruby. The Ruby who lived among the Negroes, whose family mixed with them; a
daughter of what respectable Whites call "the lowest of the low," that is a White
whom economic scarcity has forced across the great color barrier. All the things made
the respectable people of Scottsboro insist that the Negro boys must die, had meant
nothing in the life of Ruby Bates.

According to the author, what is the main issue at stake in this case?