Scientifically speaking, I would expect that pattern of habit to be studied, and for individuals to be unable to quit, and for actual electro-chemical rewiring of the brain (as nicotine,caffeine and harder drugs do) to be established.

Until then, why can't it just be called a habit? addiction very strongly implies inability to quit. Have you seen the 90's congressional testimony of tobacco CEO's all swearing on oath that Nicotine isn't addictive? That's how strong of a case you have to make for an addiction to be established. If you dilute the term and use it anonymously with "habit" then actual addictions can be dismissed or crooked people that facilitate addictions can avoid consequences.

At the very least, there needs to be a pattern of inability to quit the habit. Positive reinforcement signals are not in themselves indicators of addiction (case in point: LSD/Acid -- it isn't considered addictive, neither is good tasting food on its own).

I disagree, consider someone who is rich enough to afford a heroin addiction without ending up dead, in jail or institutionalized. They may never have a rock bottom that makes them question their use and try to stop. Their quality of life might drop, they may lose friends, family, business, etc, but they are insulated from the kinds of real pressures that force people without means to stop.

I would not say that person does not have an addiction. They are just as much of an addict as the person who shoots heroin and can't stop despite being broke, arrested for stealing, etc.

Addiction and mental illness tend to be defined by their impacts on people's quality of life and impact on functioning, whether that is just functioning basically, maintaining long-term healthy relationships or just being happy without substances.

In your example, I agree with you, they do have an addiction. It does not contradict with what I said. The person not needing to stop and their inability to stop if they tried are two different things. Heroin does form a chemical dependency, where it could even be life threatening to quite cold-turkey, and therefore it is addictive.

Unlike mental illness, addiction is defined by formation of a dependency. sometimes that dependency is at the biological/chemical level, sometimes it is a psychological dependency (can be caused by mental illness), not nevertheless a dependency must exist that prohibits the addict from functioning without the cause of the addiction. Bad habits can cause adverse impacts just as addictions can, and addictions (like coffee - which forms an actual biological rewiring/dependency, people get severe migraines when trying to quit it) can be harmless unless you're trying to quit.

I don't think this is correct. I believe the clinical definition of an addiction requires it to be actively harmful to your life - meaning, if you're "addicted" to something but it's good for you, it's not an addiction. Because the addiction part requires you doing something self-destructive.