Hey, if there's any reason the two books of the Corinthians exist in Scripture, it's to let us know that while a major transformation already took place in the lives of these folks (1 Cor. 6:9-11; 2 Cor. 5:17), they were far from injecting that inward transformation into their relationships (tolerating a man sleeping with his father's wife--1 Cor. 5:1).
Do you mean to say that "presto, upon conversion, all Christian male teens & young adults are thereby not bothered by easy access to porn since we've changed their hearts & minds & therefore why bother changing porn laws?"
If a Christian is "bothered" by porn, what he needs is not a porn law. And a porn law will not address his sin problem.
Some of the Corinthians were bad christians. Paul, if you noticed, wasn't happy with them.