Why hearing actor for deaf character?

What's the bright idea of hiring a hearing actor to play the deaf character in this film? Is it because there's no qualified deaf actors who could fit the bill perfectly out there? Think again...

Think of Mr Wrench, a deaf hitman, in the TV series, Fargo, who was played brillantly by a deaf actor, Mr Russell Harvard.

http://www.imdb.com/name/nm2341751/?ref_=ttfc_fc_cl_t23

Hiring a hearing actor for the role of deaf character is as worse as hiring a white actor for the African or Native American characters.