I don't entirely believe that. I feel like there's a certain time and place for everything in a story. What makes a story bad is bad character development. When you make a character do what they're not designed to do, it destroys the whole lore of its world and basically, you'd be better off doing this with your own made up characters. Take Eggman for example. Why would he ever have kids? He's hell bent on his own plans, why would he stop, fall in love, bang a few kids out and continue on? Doesn't make sense. Don't make something do what it wasn't designed to.