Giuliani's answer is really a red herring. Of course bishops have a right to their opinion. But that's not the question. The question is, Do bishops have the authority and obligation, under Church law, to deny Giuliani communion?
Well, that's A question, all right.
But it's not THE question.
THE question is, "if the bishops have the obligation to deny communion to Giuliani (and all the others), then why don't they do so?"