the problem with saying, "Yeah there should be enforcement, but not by the government" is that you are in the same sentence saying there *should* be enforcement, but we aren't going to provide any, anywhere. The fact is, there are bad parents. But game industry supporters sitting around saying "it's not my fault! It's bad parents!" is just as hypocritical as parents not doing anything about it. The argument against any sort of institutionalized enforcement ultimately says "people are going to be bad anyway, the government has no place trying to stop that." In that case, why do we bother making things like bank robbery or murder illegal? People still have to make their own choice about whether they are going to do it or not.
Now, Entropy, you've made that argument many times before. You seem to think there is some sort of substance to it that is meaningful to this sort of debate. Speach is protected because it is meaningful. REading a book, (or watching a program, or playing a game or hearing a speach, etc etc) isn't going to make you kill someone. Reading several probably isn't, unless you're an instable personality to begin with. I don't think anyone with an IQ above 2 is claiming that, so in one sense your argument is simply a strawman argument.
On the other hand, it is inarguable (ok, it is arguable, you'll just look foolish) that the media you take in has an influence on you. Arguing that it doesn't means that it's irrelevant what sort of things are said, so it really doesn't matter if it's regulated or not. I accept people who argue in light of this that it still shouldn't be restricted, but people who say that media has no effect on the viewer are simply ignoring reality.