For what my internet opinion is worth, find a place to work with a culture that meets your professional standards, you're not going to create a business case in favor of professionalism that persuades your current employer.

Since it is already obvious that the person will be fired and yet it hasn't happened, company culture issues perhaps run deeper than you are in a position to change...e.g. an engineering culture where it is believed that a second set of eyes on work product is not just normal professionalism.