Question

Why might deaf parents react sadly when they find out they have a deaf baby?

Answer 1

Because they want different for their child. They want their child to be able to be able to hear what they can't. And enjoy the many sounds of the world. The parents already know how much they want to be able to hear, and become sad when they find out their child can't either. 

Answer 2

Some parents want a "Normal" child,but you can't control that. They of course want their child to hear, because thats a huge part in life. Hearing doorbells,alarms,announcements,screaming. Most deaf people are mute (not all) so their child may not speak even going to speech classes. Also they may react sadly because their child will never hear their parents voice (unless implants help)