I don't think the cruise control argument is so clear cut... I think it depends a lot on your application. Yes, I agree that a human being concentrating hard on maintaining a steady speed while allowing the speed to alter slightly on gradients will probably achieve better fuel economy than cruise control.
However, after a day in the saddle, having done hundreds of miles, sitting on an empty motorway in the middle of the night it is very easy to let your mind wander and see your speed increase or decrease by 10mph or so without you noticing. Or it is for me anyway... if you're able to maintain an exact speed mile on mile for hundreds and hundreds of miles then well done, but I'm not able to do that. In those situations, I suspect cruise control would improve my fuel economy.
But also, it's more about comfort anyway... it's more relaxing to sit on a bike on a motorway for mile after mile not having to concentrate on the throttle. Or at least, it makes motorway miles a lot easier in a car, which is my previous experience of cruise control. I suppose you could argue that having to concentrate on the throttle keeps you more engaged and thus safer, but I could also argue that it is more likely to mentally tyre you out which is less safe.
Another personal preference thing really... I know plenty of motorcyclists who love having cruise control and plenty of others who hate it. But I just know that getting a car with cruise control really improved my driving experience when it came to doing high motorway milages, so I anticipate I would feel the same about cruise control on a bike.