Pornography provides sexual pleasure in a completely safe and accessible format. No STDs, no risk of pregnancy. For millions of people, masturbation may be their only source of sexual gratification. The human body and human sexuality are beautiful, and as long as it is produced in a way that does not seriously harm or degrade the performers (and I do believe that's possible), I think it's a net positive.
As a feminist I do not appreciate most pornography because it tends to degrade women. But perhaps the type that is not so degrading and that offers no violence or use of children as sexual objects can help assuage the feelings of some men who would otherwise be taking out their fantasies on real people. Decent pornography can also be a relationship enhancer.
Pornography offers no public service at all. It can offer personal gratification to some. It may offer repulsion to others. It may spice some things up in the bedroom for others. Porn has some benefits for people on an individual basis but it does not have any benefits for society as a whole. The idea that it offers any valuable public service at all is a joke. Since when did getting off become a public service?