I don't think people are understanding the point of this post. If you're like me (a responsible adult gamer), your 3DS will most likely remain in perfect condition during it's lifespan, making my concern ignorable. But, but, a lot of frugal gamers might buy their 3DS used from their local game store, and then there is no control over the condition. Read my first post, and most will understand, that if you place anything over the surface of a 3D effect, the effect is ruined completely. You go to Imax to watch something? Pop out the right lense of your glasses, and report how your experience was. If somebody took a paintbrush swipe with white paint (a scratch on the 3DS screen by ration comparison), you would immediately notice the flaw in the 3D effect, and most people would demand their money back.
Simply put, the 3DS will not allow for any user-induced damage to the 3D screen, because any flaws WILL CERTAINLY DETRACT from the 3D effects, making it far worse than the usual dead/stuck pixels, dust under screen, and scratches that we can all overlook on our current DS models.