This is only more the reason for more regulations to attempt to stop this sort of behavior, and I think the companies that are attempting to skirt these rules should be held liable for the problems that they're going to cause down the line because they won't ensure that their site (to the best of their knowledge) isn't being used by those under 18. Companies know exactly what they're doing and they're reaping the rewards of letting underage people gamble, though they should soon face the legal consequences.
This argument also applies to porn sites.
All online casinos can do is to put a disclaimer/warning sign since they cannot hire a bouncer to keep out underage people to enter.
What is your idea to solve this problem? KYC?