I find this surprising. Aren't there any rules about having to serve everyone equally? Like non-discriminatory rules? A Casino could unilaterally bar entry to all people from a certain ethnicity and they wouldn't have to justify themselves? Is this true for all businesses?
It's really fishy that Casinos can say you can come play here unless you win.
Ethnicity is a protected class, so no, you can't just ban people based on that. "Being really good at gambling" is not a protected class.
Counting cards isn't considered cheating because you're manipulating numbers in your head and in NJ, where the case happened, you can't be asked to leave a casino just for counting cards. Edge sorting is considered cheating as it's basically a form of marking cards. (This is an oversimplification of the rulings in the US
Of course, kicking you out is the only thing they can do. They can't take your earnings, prosecute you, detain you, or use force unless you resist. Usually the player will be kindly asked to cash-in and leave.
Security can track your play patterns, your gains and losses. Card counting result in very characteristic patterns, and if your gains are too consistent to be explained by chance alone, they are going to watch closely. If you are just lucky, they will offer you free drinks, if you are an advantage player, you will be asked to leave, if you are a cheater, you are going to have problems.
Edit: I think there are some places where casinos can't just kick people out for no reasons. But anyways, there are ways of making card counting impractical. The use of continuous shuffling machines is one of them.