As we know that Gambling is prohibited in certain religions including Islam. If anyone does it, the earned money is not legal and is considered Sin.
But what if someone is promoting a gambling site on social media etc, will the money earned from it be legal provided he will never directly gamble ?
I can be wrong, but I think that gambling is prohibited by many religions because this activity can potentially:
1. Make you greedy;
2. Harm you financially.
Greed is a sin because once you are possessed by it, you can't think of anything but your profit, while it is supposed that you should think about God in the first place.
When something harms you financially, you can end up losing your health or even your very life, and suicide is considered a sin in the Bible and the Quran, and, I'm sure, in other religious books too.
If you are earning your daily bread by promoting a gambling site, this activity can not be considered a sin because you need to eat to survive, and you have to somehow earn money for that. Similarly, it's not a sin to work in a supermarket where they sell pork or to work in a gun shop, although eating pork and killing is a sin.
Surely, there can be other interpretations of the holy books, but I don't give a damn about what religious fanatics say. In other words, that's just my opinion, I'm no preacher myself.