I don't understand what is hurting you.
Are you squeezing it too hard? Or is it from the actual wrist movements that presumably you are performing over-enthusiastically.
If it is neither of the above then I don't know what's wrong with you, I have a friend who has incredibly weak wrists (might be something to do with her bones I can't remember) which could mean even average Wiimote swings cause pain (although being careful with it for a while could probably help to train your wrists)
If this isn't just a joke thread and you are getting pain from swinging then sorry but it is not a design fault and you have absolutely no case against Nintendo.