This case with Sportsbet is another example that fits quite well into this discussion. And it shows, what a powerful tool KYC can be and how gambling sites can use it to their advantage (not claiming that Sportsbet did it here).

There is multi-accounting and multi-accounting, this is the bottom line. If you are multi-accounting, but always lose all your money, then you are allowed to multi-account. If you are multi-accounting and winning, then you will be a victim of T&C's.
I am 100% sure that every casino/bookmaker knows about a lot of players doing multi-accounting at their sites - and they are fine with it, as long as it's giving them profits. If these players start to win, hit a bigger parlay or request a withdrawal, they can always user their power-tool, so this is a worthwhile, nearly risk-free, business, where you can never prove the operators being guilty.

Even if you choose to voluntarily do KYC once you opened your account, you are not safe from running into trouble in the future.