Internet Gambling Illegal?

Why does internet gaming have to be illegal. If people are able to go to casino's and gamble what is the difference by them being in their homes doing the same thing? I think that all these casinos had a big influence in this. They don't wan't to lose money. By people playing and betting online they are not going to the casinos and spending their money there. This link im putting is an interview on 60 minutes talking about why it is illegal.

www.cbsnews.com/stories/2005/11/17/60minutes/main1052420.shtml