The answer to that question is simple, banning legalized and regulated online gambling in any form, just makes another way for organized crime to get a hold of peoples money, and then no one but the criminals wins.If you want to keep a child from seeing an R rated movie you do not ban the movie from the theaters do you? No that would be silly you just make sure that people are doing there best to check and verify that no one under 18 gets into seeing the movie. By banning the movie chances are greater that someone will get a bootleg copy and show it to every kid in the town.
So if you want to keep a child from gambling online then all the online casinos should be regulated and monitored, not banned.
The same goes for terrorists. If you believe terrorist groups are exploiting an unregulated and unmonitored industry such as the online gambling industry, then by regulating it you can see where the money is going and make sure it is not going to fund international terrorist attacks. All that is accomplished by banning it is that the criminals get a stronger grip on the industry.
The ban on online gambling is much like the war on drugs. If marijuana was legalized in the USA crimes related to it would almost go away completely, because it would be sold in stores and it would be controlled, another advantage would be that people would no longer be going to jail for marijuana-related charges, this means thousands of fewer people getting arrested and going to jail every year, which would save us tax money that could be better spent.
By making online gambling in the USA a legalized form of adult entertainment it would also bring in an estimated 1.2 billion dollars in taxes to the American government. This money could be used for schools, police and universal healthcare for all Americans.
This is how you improve society, not by telling people what to do. It is human nature to want what we can not have so the more laws you put in place to stop people from doing something the better the chances are that people are going to do it.
