Because music is a creation of vibration, it is all of us (since we are all vibration). When we sing off key it is most often due to the fact that we are not listening carefully to the music. Sometimes it is necessary to listen to a melody repeatedly before learning it properly to sing it. There is a tiny percentage of the planet which is actually tone deaf. The rest of us, well, we're basically not trying hard enough. If you love to sing, but fear the criticism of your voice, I encourage you to memorize a song, note for note. You will, most likely, surprise yourself when you put in the work, pay close attention, and use the wholeness of your mind.