I disagree. Fun is what you make of it. I can see myself having fun riding a hybrid with big balloon tyres. And upright riding position doesn't mean you can't have fun. I had plenty of fun trying out unicycles for instance. I think I might get one. I ride in a fairly upright (by roadbike standards) position on my MTB and I have fun too. I gave one of those chopper bikes a whirl too and had fun. There are plenty of ways to have fun on a bike and not all of them dictate that you have to be in an aggressive aero position going balls-out at whatever speed you can attain with your derailleurs pushing your chain as furthest outboard as can be.