Well, first we ask Websters to define this(cause I like definitions, but some people don't so I hid 'em)
Then a handy one by dictionary.com
If we're talking about the first then no, it's not a disease. The same thing goes when someone say 'Oh, I'm addicted to [insert activity, action or object] they probably don't mean that they're truely addicted by the other definitions. It's not compulsive and they have no control over it.
However, if it's a compulsion that they can't control, yeah that's bad. A disease? I dunno, really, I mean, I firmly beleive that if you want to stop something you can. Will it suck? Probably. I was addicted to caffeine, the actual compulsive, psychologically damaging, etc version of addiction. I beat that addiction and it sucked. Do I think I had a disease? No, just a problem.
I will admit, I sometimes think people use the 'disease' card to get out of being held responsible for how they acted or behaved. I know that not everyone can beat an addiction on their own, and I fully support people that fight to curb one, but I'm not going to give them the easy out of 'oh you're [sick]'.