I live in Las Vegas.
Card counting is not illegal, and is not a posted prohibited practice at casinos here.
It IS a discouraged practice, and those who even appear to be making the attempt to count cards are often removed from the premises, sometimes permanently (picture taken, name written, and info IMMEDIATELY sent to all other casinos in town).
Casinos are not businesses. They exist only to make money, not to offer a product or service. Anything you think the hotel is providing you with (that room, the steak dinner, tickets to the show, valet parking, a pool, etc.) are only there because the casino feels that it will somehow help them to seperate you from more of your money, and do so in a more discreet fashion than simply having goons lift your wallet. In the end, there is a lot less legal hassle when someone voluntarily hands over their money.
A word on card counting and why it is not illegal: it cannot be legislated, or within the rules, to delineate that only people with a sufficiently low IQ may gamble. I do not gamble, but I have played blackjack with friends, family, etc. in the past. It would be impossible for me to turn my brain off so that I could not remember that all 4 Kings and Queens had already been seen, but only 1 of the Aces.
Casinos also do not offer gaming without being SURE that the odds favor the house. And I don’t mean like the house wins 60% of the time. A quick call with the Nevada Gaming Commission years ago confirmed that most casino table games (which excludes video poker and slots) have an average house win % of something like 80%. The gambler is at a serious disadvantage because of the rules of the game he plays… no casino will even offer a game unless it is already assured of profitability.
Bottom line: card counting is neither illegal, nor even morally wrong. But since casinos are not in the business of offering games of skill to willing players, but rather are there to take as much money as possible away from the people who enter the establishment, they will do everything they can to discourage the practice and prevent those who do possess this skill from entering.