The captain should always make the decisions and the FO should always as 2nd in command support him unless he can't because it puts the flight in jeopardy, then it is his job as a crew member to protect his crew and passengers to do what ever is neccesary to protect them. Never let another crew member put your flight in jeopardy. I don't care what country you live in. This is a pilot's responsibility to his crew and passengers, not to his airline.