These same casinos try to keep minors out, but some invariably slip through the system. Contrast this with a virtual casino. When one plays electronically, each bet is closely monitored. With today's financial reporting, it is possible to verify a bettor's age, identity, and spending history almost instantaneously. Software now exists which allows people to lock themselves out or set loss limits.
Many sites have their own limits as well.
Many do not accept credit of any kind. As to integrity, technology now exists that allows regulators to randomly audit web sites to ensure the fairness of the games. I would like to take on one serious inaccuracy that frequently appears in the rhetoric of anti-gambling advocates. They often portray a scenario in which a child borrows the family credit card to access a gaming site, and gambles away the mortgage money. That would be truly appalling if it were accurate.