With gambling at the beginning everyone decides of placing small amount, but if winning take place then automatically mind becomes greedy and makes the gambler to go for big amount. This at times described as sickness as well addiction when the person doesn't have a mind to concentrate upon other activities similar to a day job.
Yeah the house edge is really earning a lot of it and for me not the gambling itself is considered as sickness. But the gambling addiction is the one making a gambler being sicked.
And it is the sickness that is very hard to treat because there is no treatment for that kind of sickness.