Like everything else in airlines whenever there is a limit for something e.g. MEL,FD, FOD, there is now a target. whatever the intent was for a limitation has long been discarded and a binary choice has now been presented. That choice is "are you legal, yes or no?". Too many PIC's have been kowtowed into following the company line but if they understood their legal responsibilities then they would realise that standing firm will not get you fired. As clearice stated an F/O has to also stand firm if they believe the situation is compromised. The only way you get to be a captain that stands up to the company is to be an F/O that is prepared to do the same.