I think what this comes down to is "you can't legislate morality". Morality exists within a person, and it is costly to build up. You can't write a law that says people are now moral anymore than you can write a law which says that people are now wealthy. Trying to do so will not work and will have bad unintended consequences.

I like to think of porn like alcohol. A little bit is not inherently damaging but too much is, Children should not have access to it, and a healthy society is one where people can have it but mostly choose not to.