I don't think everyone can learn to sing passably. I've met a partially deaf person and a "mentally challenged" person who were both just plain irritating. Everyone else I've *ever* heard was somewhat pleasing to my ear...but singing well? That takes years and years of practice, as well as physical ability and musical talent. A good warm-up also helps.

I think the hardest thing to do for most beginners is to concentrate on the music instead of the emotion. It feels awful not to concentrate on the emotion, but concentrating on the music will eventually pay off.