I completely agree with you that restriction does affect discernment in terms of exposure and development of faculties in children. That being said, I think parents have a prerogative to do so. Much as I might want to deny it sometimes, we are all products of our parents, our families, our upbringings, and the societies in which we are raised and what's available to us. Depending on how restrictive and what the social values of different parents are, that will affect the upbringing of children, but it should still be the determination of parents and not a paternalistic regime where government regulators are able to decide this.
On March 11th, 2008. See this statement in context.