We'll creating or having two or multiple accounts should not be the reason why gambling sites choose to block accounts but yes sometimes some open multiple accounts to carry on illegal activities so I believe if it's in this perspective they ought to block more than one gambling accounts.
Why do you think having multiple accounts shouldn't be the reason for a casino to ban or block the gambler's accounts? Do you mean that it's okay for someone to have multiple accounts and a casino shouldn't do anything as long as they aren't trying to do something illegal? How would they prevent bonus abuses then?
Someone with multiple accounts can easily abuse bonuses and promotions provided by a casino by joining with all their accounts. It might not be illegal but it's unethical and it's against the rules, so it isn't allowed and it shouldn't be allowed. Hence, having multiple accounts should be a reason for a casino to ban a user.
I know the feeling, bro. Multi accounting can really mess things up, especially for those casinos that give rewards to the referrer based on how much you gamble. It's true, it can give an unfair advantage and mess with the house edge. But yeah, it does seem a bit two-faced for casinos to enforce this rule just when someone hits a big win. They should at least try to come to a fair agreement instead of just shutting down the account.
It's fair enough to say that a casino shouldn't allow it in the first place and the accounts should be blocked immediately when the gambler creates two or multiple accounts, but why does a gambler have multiple accounts in the first place? If you have multiple accounts, and you hit a big win with one of them, and then the casino investigates and finds out what you have been doing, they have all the rights to ban you or confiscate the funds.