this article from 2010 several of the points of view were raised.
My personal opinion is that of course there is a restriction matter and we should be aware of what is being done to enforce it. Parents are the very first defense line in this case, no minor could buy a video game by themselves if they don't work for it. Since money is involved it had to come from somewhere and how is it being spent should also be a concern of the parents. If these principles are enforced since a very young age parents would have nothing to fear.
Blaming game developers for the content is just an excuse from people not wanting to be responsible of their own actions. Blaming retailers for selling a product they are meant to sell is just contradictory. There is a parental advisory on the packaging already which is pretty standard in all entertainment media. In video games the rating is pretty elaborate an it goes from "E for everyone" to "M for mature" and it was put in place by a gaming company called SEGA after they were criticized for releasing Mortal Kombat with a secret code that let you see "all the good stuff".
In the end its hard for families that both parents work to have an eye 100% of the time on the kids and what they are doing; but households should always have certain rules that must be respected by "E".