Must Educational Games be Fun?

In a brief article in the online Chronicle of Higher Ed, an interesting session of the recent Serious Games Summit was recounted ...

Mark Prensky:

argued that instructional designers often do more harm then good when they work on educational games. 'Whenever you add an instructional designer to a team, they suck the fun out,' he said. And he argued that if players of educational games don't enjoy the experience, they won't be engaged in the activity, and therefore will not learn much.

Jan Cannon-Bowers:

said that she does not care whether a would-be pilot who uses a flight simulator has fun or not -- she only cares whether he learns the necessary skills. And she said there's a better chance that games will be educational if an instructional designer is involved.

So why are we instructional designers thought of as fun-suckers?