Schneier's point is not only that those attributes should be ignored, but there should be no correlation between those attributes and the end result of the algo

Schneier's point is not only that those attributes should be ignored, but there should be no correlation between those attributes and the end result of the algorithm. You can quite easily find examples of algorithms which do not include race or gender as an input, yet have a disparate impact. Schneier is saying that algorithms with disparate impact should be avoided without regard to procedural fairness, proportionality of outcome, or correctness.