There is widely cited “research”, quote/unquote, in line with your statement that the effects on the brain are like addiction, such as to heroin. Perhaps the best answer to that is from Nicole Prause, who was formerly at UCLA, a neuropsychologist, who has pointed out that the effects on the brain of viewing pornography are similar to the effects on the brain of viewing a picture of a loved one. Dopamine and other chemicals are not distinctively associated with addiction or with viewing pornography. They're often distinctively associated with positive events.
You're also touching on the issue of, quote/unquote, “sex addiction” or “pornography addiction”. In fact, one of the briefs before you is by a so-called certified sex addiction therapist. I want to emphasize that the American Psychiatric Association's gold standard manual of psychiatric disorders, the Diagnostic and Statistical Manual of Mental Disorders, edition 5, a fairly recent revision, explicitly considered and rejected both the diagnosis of hyper-sexuality and sex addiction. The American Association of Sex Educators, Counselors and Therapists, the largest organization of sex therapists, has dismissed the idea of sex addiction.
Clearly, there are people who use pornography or many other things in an intrusive and compulsive way that interferes with their life, but the concept of addiction or unique neurochemical events is not one that has much support.