Keep in mind that just like TV, movies, and books, video games are created for all types of people -- not just for children or kids. It would be best for the children not to play those M rated titles anyway, instead of having Valve sacrifice its core adult male userbase in order to teach children about cheating.
I don't think Valve needs to be held responsible for children's morality; I think that job still rests on the parents.
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No longer around. Thanks your support, everyone! As always: