Dunmurderin'

I can't speak for everyone, of course, but I think maybe it's fun for the same reason that it's fun to daydream about "what my life could be," or for the same reason that it's fun for a small child to invent an imaginary friend or an imaginary world. It's fun because it's fantasy, it's an escape from the real world and its troubles, and it's a chance to be silly or smutty or totally on crack or any number of other things that one might never dream of being in the real world.