The only way I can really agree with the argument that more games should have the AO rating is if the rating wasn't seen to be the worst of the worst in everybody's eyes since that's what the AO rating pretty much means now. What's worse is that the AO rating isn't even supported by the usual retail stores and the big 3 so what would happen if Gears of War and Resident Evil 4, two VERY popular games, got the AO rating instead of M?
In fact, I think the way the games are rated is flawed. Like others have said, some games were probably rated too high and could have made a lower rating. I think what ought to happen is a massive reform of the system to better rate the games while at simultaneously providing a better way to provide information to parents, retailers, and the public to help educate others so that they can make better purchasing decisions.
That said, if M games are the equilivant to movie's R rating and their content isn't ment for children, I'd rather not have the mature games be targeted by the population since that is the intention of that rating.
