I believe that you need a casino license in almost all countries in the world.
So the answer in NO. It's not legal to operate a casino without a gambling license.
Of course that doesn't stop you from creating one and trying to get customers.
Many businesses stay in the greyhat/blackhat area, but there will be consequences sooner or later.
I think that having a gambling license isn't a guarantee that the online casino won't scam the gamblers, but it's usually better to pick a casino with a license, if you are a gambler. The license kinda gives a false sense of security and the illusion of dealing with a legit business.
If you want to create a casino, try to get a license, otherwise you might have problems with the authorities.