If a referee is unconsciously biased, then he's an idiot. It's like excusing a judge for having unconscious bias and putting black kids away while letting white guys go free for the same offenses. Bullshit. Their job is to be conscious of their biases and to manage them. If they can't, bin 'em.
FWIW, there's no way I can ever be convinced they they have any unconscious biases. They know exactly how they feel.