How is porn wrong by nature. Sex is the most natural thing two human beings could partake in.
Porn is one of the reasons relationships break-down. A man has a wife whom he's happily married to. He watches porn and starts to develop lustful thoughts. Now when he goes back to his wife, do you think he will truly feel the same way?
Porn doesn't just affect relationships, but it can affect people finacially too.
However I will say that it is up to people if they want to watch porn or not, they have a choice anyway.