Umpire Decision Review System (DRS) is a highly contested system being used in today's cricketing world. Basically it means that at any time a player can ask for the umpires decision be reviewed by the 3rd umpire as they believe it is wrong.
However rule article 2.1.5 of the code of conduct states that a player may not show dissent towards the umpire or disagree with their decision. So surely using the DRS system would mean that players are breaching this code every time they use it? The BCCI has been a notable opposition to the system citing that it is not 100% accurate and therefore cannot be trusted. This stance of the BCCI has seen India not be able to effectively use it when they are forced to during ICC events and when touring.
Personally I see nothing wrong in using all available tools when playing at the highest levels where one bad decision can end a countries hopes at an ICC trophy, people make mistakes and that is where technology comes in to assist them.