Now to note before the comments below - I've never seen "Your Brain on Porn" and porn isn't an issue in my marriage because if by some miracle my H uses porn (overcoming his very strict religious upbringing), he's amazingly discrete about it (I've never seen any, I've never "caught" him) so - these comments are gleaned from an outsider perspective.
I might suggest it could be an impulse control disorder.
If you do something repeatedly despite the potential or real harm to yourself and others, its a problem. Are all people who enjoy more porn than their spouse agrees with "addicts", well, no. Not by any means. And yes, in most cases the issue is the couple in question needing to agree on boundaries - and in many cases, no the porn itself isn't the issue - but behavior and feelings that need to be worked out, potentially with professional third-party arbitration (AKA marriage counseling.)
But what about the following scenarios in which case we substitute "porn use" for obsessive gambling scenarios, :
- You are living hand-to-mouth because of how much you are spending on porn
- You are constantly risking getting (or actually have been) fired from work by accessing porn at inappropriate times
- You are tired during the day, and it is affecting your performance at work because you stay up at all hours of the night looking at porn, yet can't stop.
- You pass up on social situations and often arrange your schedule so you can make sure to have enough porn time
- You are distracted during what should be enjoyable activities (outings with the kids, dates with the wife, golf) because you are agitated and can't get back to the porn
- You resent others (including your spouse or family) from infringing on your porn use time, and might become violent, angry, or belligerent as a result
- If there was a prolonged power outage (or a natural disaster) would your primary concern be safety or shelter for yourself and loved ones or - what am I going to do about my porn?
Whether or not that's an addiction, an impulse control problem, or whatever you want to label it - the situations above have gone above and beyond a martial issue with sex. It's beginning to negatively impact your day to day life and its beginning to affect other people (particularly if its making you violent.)
It's a problem that needs to be addressed with intervention, potentially of the professional kind. And while yes, very much so there might be deeper underlying causes to what's fueling the issue, those other problems may or may not in and of themselves have a clinical diagnosis.
So - I'm not going to debate if labeling it as an addition let's people "get off easy" (which the irony of that statement in relation to porn isn't lost on me, btw :rofl

. But - if its a recognized disorder, it might mean some people with a legitimate problem that needs professional intervention might be able to better access that help because insurance will cover it and if its something that primary care doctors are more on the look out for.
And yes - the above is an extreme example. But - the examples that end up with you getting a clinical diagnosis are the extreme examples. Wanting a clean kitchen doesn't label you with OCD. Staying up for three days straight clean or not eating because you are scared to make the kitchen dirty does. Likewise, using porn doesn't make you an addict or give you a "porn impulse issue" - but when you start replacing meaningful interactions with other people, when it starts to make you violent, or it starts to affect your employ-ability - it's an issue.
Regardless of whether or not its chemically affecting your brain.