Should I be concerned about my 17 year old basically publishing written porn

My son's dad thinks I'm overreacting but I found out our oldest was posting smut online. I spoke to his dad and showed him his laptop and his dad thinks I'm overreacting and that it's normal for teens to write fanfiction. He was writing fanfiction for animes he watches. But a lot of it is so sexual. His dad says many cringy fanfictions are written by teenagers and I need to stop embarrassing him about it. I asked our son why he was writing these and he said he was doing it for fun and just enjoys writing fanfictions and makes fanart. It's not even normal sex he's writing about. Some of them are actual fetishes. I asked other people their opinions and they all agree I'm overreacting.