There's an element of therapy in 'sad'. I had a series of bereavements earlier this yearand found that talking about the situation helped immensely. This is a common experience and really indicates that 'sad' can be actually very uplifting…I know it's counterintuitive but much of life is. In contrast 'light hearted' often leaves a sense of emptiness and futility. Perhaps that's why so many sad ballads continue to e sung. But…we need to remember, 'The Whumil in the Door', 'Seven Nights Drunk' and many of the Robin Hood ballads which are amusing, lively and have happy endings and are all in Child.