To be fair, cars really should scare us a lot more than they actually do; the only reason we don’t notice how dangerous they really are is because we’re desensitized to them. Cars kill more than a million people per year. And I’d assume most of those deaths are accidental (due to operator error or poor maintenance) as opposed to guns who generally kill because someone wants them to. 1MJ of energy is nothing to scoff at.
To give a more likely scenario, let’s say a piece of brass the size of a gold dollar delaminates from the flywheel and shoots off at tangential velocity. That piece would be traveling at ~100 m/s and have an energy of 160 J, about equivalent to a civil war rifle. That could do some serious damage if it ends up hitting someone