In this part it is the addiction and not gambling that is considered as sickness. Gambling is just a trigger device to make you addicted or shall I say sick. Another example I can say is, can you consider smoking cigaret a sickness? Lol of course no, it is the cigaret addiction, and the effect of smoking that is what we called disease. But smoking were never a sickness but a vice. So how can be a gambling a sickness and not smoking?
As mentioned many times before, addiction is the result of our action, in dealing with gambling. Though I do not consider gambling as sickness, I do believe that it is a tool that leads us in wrong path if the addiction is not handled properly.
Gambling is only for people who are aware of what they are doing and knows what their limit is.
With that said, don't think that gambling is sickness since we will not have a bad experience if we will are being responsible while we are gambling.