I think having a handful of characters with tragic background stories in a Roleplay is not only realistic, but also more interesting as well. There's an extent to this, of course, but characters with unfavorable backgrounds and psychological issues can be likable, interesting, and not complete Mary Sues if played skillfully enough. I admit that most of my characters have unhappy backgrounds, psychological conditions, and dead relatives/friends as I base them off of myself and I come from an abusive family, have a few diagnosed conditions, and have seen a handful of my friends die from drug overdose in recent years.