Why does everyone seem to think that any M-rated game is wrong for the Wii?

[Rainbird]

Personally, I think these are all different groups of people.

Those who complain about games like MadWorld and HotD are most likely people who just realized that the games available for the Wii are in fact not 100% kiddy friendly, which means there is a risk that a such game might be played on their very own console, possibly by their own kids!

Those who complain about a game releasing on the wrong console are probably either jealous of the title, or has a stereotype about all owners of the console in question, which the game does not fit with.

Personally, I want to see the Wii be succesful at hardcore games. After all, a game like MadWorld could never exist on the PS360 without losing some of the things that make it unique in its genre, namely the controls.
But before a game like MadWorld will sell well (I personally don't think MadWorld will sell all too well because of the Wii's current userbase combined with the game's shortcoming, but I hope time proves me wrong), there needs to be other games on the Wii that will attract the people who will buy the hardcore games on the system.
So, in order for the Wii to become interesting (or just for ignorant people to change their mindset about the Wii), there needs to be games out for it which will "suffer" from sales we might consider low. Although I have no idea what publishers are aiming at with a release like MadWorld, so that term is relative.