I'm sorry, but what are you talking about in your first paragraph? What you just detailed is the opposite of reality. Environmental factors have nothing to do with addiction? If this were the case, mono/dizygotic twin studies would show 100% concordance with genetics. They don't. OF COURSE environmental factors can influence rates of addiction. To postulate otherwise is to live in a fantasy world.
I don't "like studies so much." Please stop putting me in this light as someone who only bases my thoughts off concrete-evidence. I have taken electives in addiction, worked with addicts, attended open AA meetings...but hey, studies studies studies! Since I love studies, I'll cite that 0% of concordance studies (of the thousands that have been conducted) show that environment has no effect on addiction.
Brain scans show what? A still-life image of the brain. I'm going to assume you meant fMRI/PET. Now, do these show release of dopamine, including the magnitude and duration? No. They show the anatomical region of the brain that receives greater bloodflow (perceived as higher metabolic demand) in response to a certain stimulus. I have NO DOUBT that regions in the mesolimbic system will fire in response to an AA meeting. However, to liken this metabolic response to the surge of dopamine that an addictive drug creates is...unreasonable. I'm not talking about how the subjects will react. I'm talking about the actual physiologic response.
And to your last point, the drug of choice simply uses a NT release mechanism to which the individual is most pre-disposed. That has nothing to do with their increased susceptibility to intrinsically addicting substances.