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I have heard complaints about Mario Kart Wii not having voice chat capabilities and how that is a sin against fanboys and girls everywhere. (as seen in this VG Cats comic - nsfw due to penis hat reference) I have to say, for the most part - I disagree. I really have no desire to sit there and have a total stranger call me every name in the book. Let's be realistic here - Mario Kart causes large outbursts of profanity. (if it doesn't "yer doin it wrong"). With the giant amounts of items getting tossed at you (my personal most painful was the Blue Shell/Lightning/Ink combo one after the other) you are bound to want to question the lineage of the other players. Loudly.
Nintendo finally seemed to cave in and be labelled the 'family' system and markets it as such. Do you really want to go online to risk your grandma or your little brother getting profaned at? Not so much, then Nintendo would just catch crap about 'Oh, this is terrible, you marketed this as a family system' - when, in fact, they have absolutely no control of what people will say to one another. The only viable option was silence.
Personally, I would have liked an option where I could hear my friends and my friends only. Then, I could call my friends whatever I want (and vice versa) as they have earned the right to be sarcastic and mildly abusive (as that is how we do). This would also work for families as you can see what friends are in the Mario Kart online room with you and deal with them accordingly if they get out of hand.
As it is now, my friends and I are installing Skype on our laptops as a stopgap so we can get on with yelling at each other or laughing at each others misfortunes. It's an extra step, but one we are all willing to make.
Side note: I play Waluigi on Wario's Bike and for some reason his voice seems to be louder than many of the other players, so I often get a kick out of that. He already says plenty by himself, without me adding to it.