Is it possible and legal to open an online casino without a license?
It is possible. It is not legal if you intend to operate in most countries of the world.
It would be seen as a scam casino. Even it is a scam casino. If you want your casino to be legit and not a scam one, you need a licence for it.
Like freebitco.in you mean?
You have quite a few casinos without a license here:
Information of Crypto Casinos License and KYC requirements That are not scams AFAIK.
You need a license to legally serve gambling products to some jurisdictions like the UK and the US.
You don't need one if you open a casino in a territory that doesn't require you to have one (I think a lot do though) and serve countries that don't need you to be licensed there in order to operate. Just search if you need one for your country.
What you say is quite useful for the OP but you forgot to say one thing: in the UK and many other countries, especially in Europe, it is not enough to have a Curaçao license to operate in them. You need to acquire a country specific license:
Apply for a licence to operate a gambling business.You need an operating licence from us if you want to provide gambling facilities to players in Great Britain (England, Wales and Scotland).
What many cryptocurrency casinos do is to take a license from a tax haven and then put in their TOS that they do not accept people from England, Wales and Scotland, and many other countries, when in reality they turn a blind eye.