Why is card counting considered illegal in Blackjack?
Card counting isn't considered illegal. Casinos have the right to deny service to anyone, and of makes sense to deny players from playing a game in which they have an advantage versus the house. This isn't  cheating in any sense of the word. 994 P.2d 1151 (2000) CHEN v. NEVADA STATE GAMING CONTROL BOARD and Monte Carlo Resort &amp; Casino:


  This case presents a conflict between two inconsistent public policies that have developed over the years with regard to the gaming industry. On one hand, gaming establishments have the unquestioned right to protect themselves against so-called "card counters" who have developed expertise in the game of "blackjack" ("twenty-one"). On the other hand, neither card counting nor the use of a legal subterfuge such as a disguise to gain access to this table game is illegal under Nevada law.


cheat transitive verb


1 : to deprive of something valuable by the use of deceit or fraud 
2 : to influence or lead by deceit, trick, or artifice 
3 : to elude or thwart by or as if by outwitting  intransitive verb 
1 a : to practice fraud or trickery b : to violate rules dishonestly   [...]