I type medical reports. Just became somebody is diagnosed with a disease, they do not have to accept treatment for it. And some people with some diseases (like hypertension or diabetes) can decide to lose weight or eat healthy - such that they can then stop taking medication for it - or they can just stay overweight and eat unhealthy and keep taking medication, or they can choose to do nothing. Or someone diagnosed with high cholesterol numbers can change their eating habits and lower their numbers, or they can keep eating the way they do and take medication, or they can do absolutely nothing. (NOTE: SOME PEOPLE RESPOND TO BEHAVIORAL/DIETARY MODIFICATION.)
For these diseases, I do not believe that an outsider can "force" a person to get medical treatment. But for diagnoses such as dementia or Alzheimer's or mental illness, family members can get "system" permission to force treatment or force a person into the hospital or nursing home setting.
Is addiction a disease? Maybe the benefit in classifying this as a disease is that the legal and medical systems are freed up to sometimes have the authority to "force" treatment. And how many times has forced treatment been an instrument in breaking through the denial of our loved ones' (and even our) denial.