Do you think the gambling population would see it as a fair system or they would evade paying the tax?
I even agree that it would be fair if this charge were applied only when the person is going to make a withdrawal.
At this point, the casino must calculate everything the player has already invested (put money into the platform) and how much he is withdrawing...
So, the tax should only be paid on the profit in this operation and never on an isolated gain in a single bet... that is really unfair.
If it were done this way, I think the tax would be very fair.
Another way would be to charge a fixed tax on all and any money that is deposited into the platform. But then, no more tax should be charged during the bets (whether winning or losing) or even during the withdrawal, since it was already charged at the source.