First, almost no deaf people are mute. That word means unable to speak because of having no voice and Deaf people do have voices. Since they don't hear themselves, they tend to be very loud. The dining rooms at the school for the deaf were almost as noisy as a stadium during a big game.
I've only known one person who was born mute, although I have known a few others who had their voice boxes removed because of cancer or other problems. That mute little girl had deaf parents and nobody knew she had no voice until she entered grade school because her family used sign language at home.
I assume the person who commented was able to become friends with deaf people because he or she knew at least some American Sign Language. It's a good thing ASL is now recognized as a real language and taught in many schools.
Second, one of the greatest insults to deaf people is being told someone pities them. Members of the deaf community don't consider themselves disabled and, unless they weren't born deaf, don't realize what they're missing by being unable to hear. They see hearing people hold their ears or flinch at certain loud noises and are glad not to experience those sounds.
Third, there was nothing noble about us raising our foster kids.
Imagine that a couple fluent in German knew some children whose parents had rejected them because the kids would never be able to learn any other language but German. If the children seemed normal otherwise, it wouldn't be a big deal if the couple took them into their family. That's how children who could only use Sign Language seemed to my husband and me. Like many two year olds, children at the school where I worked often had tantrums because they couldn't communicate, but stopped having them once they learned to sign. We expected to keep the boys permanently and by the time we realized their tantrums had more serious causes, we considered them our own.