Most of site won't tell you first when you signed up. It stated on their rules, but i think most of us don't aware there is KYC or not. I usually check their rules first whatever we need KYC or not before deposit my money, but i won't deposit if there is KYC stated since i don't want to give my details only for some bucks.
Yups that is the dark side of each site (though not all has that) they're KYC rules implied in their TAC that in time of Having questionable activities they will require us of providing KYC in which most of the time they are using against us, because they Knew that majority of us Hate giving our details so the case will favor them in one side .
and for me this is not literally rules but Cheating that Hides in their so called Rules.
I do not think that its "dark side" of the casinos, I just think they put those things into their rules because it is not something that will be done all the time. What is the point of saying "we will ask 0.01% of you for your KYC" when you sign up? Plus their rules are available for people who did not sign up, so you can read it before you do it and that would be fine as well, that way you can get to learn more stuff and it would be fine for you.
Why would you want to end up spending time over being upset on what is going on and about the rules after you sign up if you care about it so much? Just read it before you sign up, it is not a secret that they hide from you, it is something that you could check. That's what I do, and KYC was never asked from me in most places that I gamble, actually I do not think that I have ever given KYC to anyone ever before.