Regardless of why the Civil Rights Act passed, the GOP through Nixon instituted their Southern Policy, which was a racist policy courting the white southerner. It was, is and always will be a racist policy.
The real "Southern Policy" was authored and crafted by noted racist , Lyndon Johnson, when he forced Civil rights legislation through Congress and Republicans supported it unanimously.
His reasoning:
"These Negroes, they're getting pretty uppity these days and that's a problem for us since they've got something now they never had before, the political pull to back up their uppityness. Now we've got to do something about this, we've got to give them a little something, just enough to quiet them down, not enough to make a difference."
The desired result:
"I'll have those n*****s voting Democratic for 200 years,"
Johnson's doubts:
"I think we just delivered the South to the Republican party for a long time to come."
Nixon had nothing to do with any of it.