Keep winning at Blackjack (however legally) and you'll be banned. And don't casinos share black lists of players who beat the house consistently?
It depends on how blatant your card-counting is. The professional ones tend to work in teams in which members sit at tables placing minimum bets and signal the “big player” to come in when the card count is favorable. Casinos tend to focus on those who consistently show up at tables to place big bets when the shoe is “rich” in high cards. Those that really know what they are doing will avoid suspicious behavior that tips off the casinos while they slowly and methodically “grind” out their winnings.