I hear this all of the time. The truth is-most people are not tone deaf. Most can be taught to sing. If a person has hearing loss, they may not be able to discern between pitches. This is one of the few reasons why a person could not learn to identify pitch.
Here is the good news-most people can learn to hear music. Hearing music is like learning a new language, the language of hearing music using their ears! Singing is developing muscles in a new and unusual and supernatural way.
And, when a person says “I can’t Sing” what do they really mean? A record label won’t sign them? Nobody will pay to hear them sing? They are so self-conscious they won’t allow themselves to sing? “I Can’t Sing” is a blanket statement that deserves to be dismantled to get to the truth.
Humans can sing-physically. At what level and awareness a person sings is a whole other discussion!