Well, you can't really pin it as an "either/or" situation. For some people, it is behavior, but for others it is genetic.
Now, technically speaking, no, I don't think alcoholism is a disease. People can't catch it like a cold or leukemia. However, I think a better term for it would be a disorder. It is a condition that is either mental or genetic that lends them towards drinking alcoholic beverages to excess and to become addicted to the effects of alcohol.
Now the genetic condition of alcoholism can't be avoided. Some people with certain biological tendencies find it very easy to become addicted to alcohol and it's effects. I absolutely believe that some people have biological tendencies to addiction.
The issue is that it's not the fault of these people that they have biological tendencies to addiction. However, what is the fault of these people is not seeking help once they get addicted.
Biological addiction tendencies can never be "cured." However, once a person learns that they have it, they need to be taught to be responsible about their behaviors and deal with things healthily. For instance, they should avoid scenarios where they may be tempted or encouraged to drink, even socially.
With regards to the behavioral condition of alcoholism, while it is not biological in nature, and therefore not fundamental, does not mean that it's easier to address. In fact, it could be argued that behavioral alcoholism is more difficult to deal with because of the tendency of the person to pursue addictive behaviors elsewhere in lieu of alcoholism. For instance, he may no longer drink alcohol, but he may do other things to fill in that behavior, such as gamble or use recreational drugs.
The reason behind behavioral substance abuse - alcohol, as well as pharmaceuticals - is because they become coping mechanisms to deal with stress.
We all face stress and anxiety in our lives. For instance, dealing with our co-workers, dealing with our boss, dealing with customers, dealing with our significant other, dealing with our friends, and dealing with our family. We have a lot to deal with each and every day.
What's important is how we deal with those issues. The best is to find healthy ways of dealing with those stressors. This includes talking calmly and quietly with each other. But that demands the other person's cooperation. When that doesn't come about, another good way is to just drop the issue. Sometimes people worry about things that they shouldn't worry about, and realizing that can lead to a less stressful life. And when it comes to a person's own anxiety, having time for quiet and to relax is extremely important.
Other ways to de-stress is to pursue activities that cause pleasure. This is why people feel better after eating, or after swimming, or after jogging, or after sexual activity - all of these things release pleasure chemicals in our brain.
The reason they do so is because it's our body's way of making sure we do these things. Eating feels good to ensure we always maintain energy. Swimming and jogging feels good to ensure we maintain our physical strength. Sexual activity feels good to ensure that we breed. All of these activities are pleasurable to ensure we maintain a healthy quality of life.
But not everybody is taught good healthy ways of dealing with stress and anxiety. This is how behavioral disorders develop. Especially when people face stressors that are too great for their coping mechanisms to deal with.
When this occurs, people will seek out ways to activate the pleasure centers in their brain to bring their anxiety down to a level they can more easily cope with. Because of what's going on in their life, they cannot pursue the activities needed to de-stress healthily. Therefore, they pursue activities that cause them to de-stress unhealthily.
This is why certain social groups such as the poor, prisoners, and the military are prone to substance abuse. The poor have to work very long hours with very little pay to maintain a basic standard of living, and so don't have the time to pursue more healthy ways to de-stress. Prisoners are forced to be with others who have antisocial and sociopathic people as well as prone to abuses from the guards, and so have very little opportunity to de-stress as their lives are in danger. Those who serve in the military are often ordered to perform actions that go against their personal moral code but are forced to do it for the furtherance of the military's agenda, and so the moral dissonance between those can caused servicemen to cloud it out through substance abuse.
This is why the poor, prisoners, and the military are prone to alcoholism and addiction to heroin and other opiates. They do not have the coping mechanisms needed to healthy live in their environments and so seek substances that allow them to cope despite how unhealthy the use of such substances are.
What's needed for these types of addicts is long-term counseling on their behavior to seek out the root of why they use alcohol and other substances to cope and to teach that person healthier ways of coping instead. This type of counseling is not easy and it's not quick, but, if done successfully, will help the addict lead a more actualized healthier life.
So if you want to use a "one-size-fits-all" diagnosis for a condition - well, you can't. And it's just plain stupid to try. And an attempt to do so is extremely unfair to those who suffer alcoholism and substance abuse and want to get help. Because if they do want to get help, which is so ****ing rare to begin with, then it's important for them to get the best diagnosis and type of therapy needed to help them fulfill that. And promoting such simplistic attitudes can only do them a disservice.