Under the [Communications Decency Act], a parent allowing her 17 year old to use the family computer to obtain information on the Internet that she, in her parental judgment, deems appropriate could face a lengthy prison term. . . . Similarly, a parent who sent his 17 year old college freshman information on birth control via e mail could be incarcerated even though neither he, his child, nor anyone in their home community, found the material "indecent" or "patently offensive," if the college town's community thought otherwise. The breadth of this content based restriction of speech imposes an especially heavy burden on the Government to explain why a less restrictive provision would not be as effective as the CDA. It has not done so.