It's just like anything else that's considered 'addictive'. It's not an addiction just by doing/viewing it, but i can become an addiction if you allow it. Some people legitimately have problems with porn and can't stop viewing it, and actually develop health and mental issues as a result
I am one of those people sadly lol. I am 1000% addicted to porn, and personally I don't mind it that much.. but it does affect my health sadly, and so I'm looking for a way out or at least to reduce how often I view it/the addiction.