A study by the Witherspoon Institute gives us the terrible social cost of porn.

From their website, they give this answer to the question of free speech and the first amendment:

In a series of cases decided since the middle of the twentieth century, the Supreme Court has narrowed the definition of what counts as obscene, and society has simultaneously grown more permissive regarding explicit portrayals of nudity and sex in magazines, in film and on television. Nevertheless, material that meets the Court’s definition of obscenity – that appeals to the prurient interest, that is patently offensive, and that lacks serious artistic, social, or scientific value – can be suppressed, while material deemed indecent though not obscene can be regulated as to the time, place, and manner of its availability. There is little question that hard-core pornography does not receive constitutional protection, even though many jurisdictions now permit its dissemination.

In their report, they give evidence for the rise in crime, trafficking, and family disruption due to our casual acceptance of pornography.