Technically, card counting is not illegal. But casinos can refuse service to anyone for almost any reason, including that they are too good at the games.
Really, there’s almost no advantage even if you’re counting cards, because you’re playing through a whole shoe just to maybe get a slight advantage deeper into the 6-8 decks the casino is using.
Successful counters work in teams, where the counter plays the table minimum and gives a signal when the count is favorable. The big money players don’t even sit down unless and until the count is advantageous. They make a few big bets and then get out, making more in two or three hands than the counter has bet all evening.
If you just keep count by yourself and increase your bet from 15 to 100 when the count is good, the casino doesn’t give a shit about you.