For adults, an ideal BMI is between 18.5 and 24.9. A person with a BMI over 24.9 is considered overweight. A person with a BMI under 18.5 is considered underweight (I'm assuming that you may get slightly different numbers, depending on the source of your information, I just picked the eMedTV website.
So it makes sense (to me, anyway) that the Wii system would allow you to choose any BMI within that range that you want to.
I also think that as an intelligent adult, you can trust your own judgement over that of a VIDEO GAME.
Just because the Wii lets you choose your character's hair color, doesn't mean it make you go out and get your hair dyed, right?
Can you not choose to ignore what a video game tells you, without dumping the video game? (Have you ever played a shooter video game, and did it make you want to shoot your neighbor? Did it make you shoot your neighbor?)
Do you really need to drop the game, because you're not smart and strong enough to make the decision for yourself whether or not to follow the video games direction? If you are happ with your BMI, can't you ignore that part (or choose to reset your goal to what YOU want it to be). If not on the game itself, surely you can just ignore it.
I'm not dismissing the possibility that some people, especially some of the people prone to eating disorders may need to avoid the scale and even the Wii. However even many people with an ED or ED history are going to be able to choose to listen to their doctor (if not their own judgement) over that of a video game (I'm not saying everyone with an ED could do it, but the culture is full of potentially negative influences, and some of them a person needs to learn to avoid, and others a person needs to learn to cope with. Only the affected person can decide which are which, whether they have an ED or not).
Should someone with an ED avoid watching The Biggest Loser or Next Top Model - or Master Chef, or other cooking shows. Should they dump their skinny and/or obese friends?
Some may have to make some of those choices, but even with a serious ED, a person has to learn to make the choices based on their current ability to do so, and that's what a person without an ED needs to do as well. Judge based upon their own ability to do so.
It's just a video game - and if you can remember that, you can continue to use it - any way you want to - and if you're unable to resist the advice of a video game - how are you going to cope with advice from well-meaning human beings. You're going to always have real people telling you that you're not losing enough or that you've lost too much. You can't please everyone, and you might as well start learning to ignore advice you don't agree with. Ignoring the video game may even be good practice for ignoring the people in your life who are going to want something for you other than what you want for yourself; because if you can't say no to a video game, how will you ever say no to your mother, sister, father....?