"Addiction is a disease" is a cop out uneducated people use to negate the responsibility of having made stupid decisions.
It softens the blow, it makes people sympathetic to those who did make stupid decisions by delegating responsibility to a factor out of their control.
This is an unpopular stance to take, because it seems mean and unsympathetic. Partially it is, but that doesn't make it any less true.
An addiction is a group of behaviors, not a disease. It seems like a disease because it is often symbolized as an activity which if continued, would lead to a decreasing quality of life, like a disease. However that's not how we classify diseases. A disease has a pathological biological process, addiction does not.
If you don't think about it very hard, it seems like addiction to cigarettes is a disease, but it's not. The pathological process that causes (for example) cancer, originates as a result of exposure to the chemicals in cigarettes, not from the addiction itself.
"But you wouldn't be exposed to the chemicals if you weren't addicted" - a non sequitur. The chemicals cause the cancer; addiction is the behavior of needing to smoke.
Also, just because it is hard to stop, it does not make it a disease. The very fact that it can be stopped with strong will power and nothing more, leads to show it is not a disease. You can't stop bronchitis or chlamydiae with strong will power, they are real diseases.
Again, "Addiction is a disease" seems unsympathetic, but alone it's not. It just calls for accepting responsibility for your own actions. If you're addicted to food and you get fat, that is your fault, you should have the will power to be able to stop yourself from eating, and you need to take responsibility for fixing the problem. This doesn't exclude the people around you from being supportive and helping you however.
Take responsibility for your own actions, have the willpower to not become 'addicted', because addiction is not a disease.