However why this 1xbit spammers are saying KYC casino is good? what I know 1xbit is a casino that doesn't require KYC, so does this mean 1xbit is a bad casino?

Well what do we expect from them? They are from the 1xbit team. They are different from the legit users in the forum so they may like things that we didn't like. Casinos that don't require a KYC doesn't automatically mean that they are a good casino. 1xbit can require or won't require a KYC but it won't change the fact that they are still a shady casino.
It will be hard to detect a fake document, that is why each KYC verification requires the users to scan their face in real time and they will follow a certain instruction. That way the system knows that they are dealing with a real person and that person is the same to the person that they see in the submitted ID.