All sites are subject to the laws of wherever they are based. They would have to comply with any court order requiring them to identify a customer (eg. suspected money laundering, handling stolen funds etc.). That's the case for all sites without any mention of it in their ToS. Is it professional to omit it?
In summary, using the definition that we are now a KYC site means that a non-KYC site is willing to violate the laws they are subject to.
It's definitely not that simple. The primary issue here is that many crypto gambling sites take advantage of KYC in an unfair manner in order to avoid paying out winnings and screwing gamblers in the process.
For example, a top site like Stake has been harassing a particular gambler using KYC as a shield. This is just one of the reasons as to why KYC is usually frowned upon.
KYC is a double-edged sword if you think about it.