You know, thinking about, I would guess that in the long run, betting probably does not pay. Except maybe for those who run the casinos. But betting is a leisure activity and as such it causes excitement in the same way as many other leisure activities do. The person who does betting could therefore be seen as a person who pays for the opportunity to participate in an exciting leisure activity.
So, speaking in a general sense, I do not see why people would object to it. Though I gather that there are certain countries of the world where betting is banned, or at least, is severely restricted.
