because people judge gamblers to be stupid people, why they risk their money to gamble, which sometimes can make all the money lost, and people think why they do not use money for investment or other business. so for good, gambling will be called a negative thing.
Actually many people when get addicted to gambling they do not think for their family and they spend all of their money in gambling that is why when someone is involved in gambling then people think that they may addict so they think of it as negative.
From what you are saying, it is like that you are saying that the gambler are the one who is think of negatively and not Gambling. Well you have a point but you did not explained it correctly. Gambling earned a lot of money from a lot of addicted gamblers all over the world. Most of them lost more than they had won, they think gambling will give you a fortune but they don't. These are the thoughts of most of the gamblers and what other people think is that gambling will make us lose our money and we have no chance of winning it the reason they view it negatively.