I think for a lot of people, porn actually stops you from acting on sexual desires. I mean, if you want to cheat on someone but you're at home looking at porn and masturbating, you will probably finish up yourself and not want to cheat anymore
For example, without porn, I would probably try to hump everything that walked when I left my house lol j/k j/k
Obviously, with anything, there are some people that are addicted to porn. But no different than anything else.
Here in the U.S., porn exists because we are so sheltered. In other countries, nudity and sex aren't so taboo.