You talk about the "net" benefit to society from porn, but do not talk about the negative effects it has. Porn has a few major downsides as it works today. 
First, the porn industry itself sucks. There is a ton of trafficking, even more taking advantage of vulnerable people, and most of the money goes to terrible people. A lot of former pornstars have called out the industry for it's problems, but nothing has really changed. We need a lot of regulations and updated ethical standards for porn production that have not been happening. Second, while porn does cause a needed release for some, it also leads to addiction and negative outcomes in others. People who consume too much porn definitely suffer for this in their personal relationships and social situations. And, on top of that, it can teach some pretty terrible lessons about sex ed and general expectations for sex. 
Now, I'm not going to say that due to all this that porn is bad and should be banned or anything. But I think it is at least enough to say that it's not a "huge net benefit". The benefits you pointed out are real and definitely big, but the weight of the negatives should be acknowledged as well. Porn is complicated, both good and bad, and discussions about it's impact on society need to be kept in that perspective if they want to be productive.