The only defense is parenting. And no, I'm not one of those childless people who tells parents to parent better.
Laws don't have to be enforced perfectly to be effective in most cases.
I don't want to scrap laws. In Britain we're 20 years ahead of the US on this (see Gambling Act 2005). Gambling laws are written by the gambling industry so no parent should think that the law will do anything to help their child.
And the UK is 20 years ahead of the US in regulation, by having introduced a law against gambling that's useless?
Okay...