The world where the gambler stops gambling doesn't exist.
No illegal alternative necessary, the players of this app get zero odds and payouts.
gherkinnn is saying that just because it is legal does not mean that the people behind the company are free of responsibility for the damage their app creates.
Casually ignoring that a large amount of gambling addicts have stopped gambling.
Also, just because people are addicted and it's not illegal doesn't make it morally right. You're still financially benefitting from their addiction.
These online casinos aren't simply complicit in their gambling addiction they are actively fueling it trying to optimize the addictiveness of their platform.